Fresh engine oil in air intake

[92carmnad2]

My engine has been running really rough, especially once warmed up at idle, or at exactly 1500 rpm.
I had new spark plugs, coil pack and leads put in a few months ago, and due to the smell of petrol I put it down to air, so I took the throttle body out (was pretty messy) and gave it a clean. However, when I looked down the pipe that connects the throttle body to the air filter I saw this:



I then dabbed a bit of kitchen roll down where the throttle body screws on:



As you can see there's all engine oil up the intake.
I then decided to check the oil level:


(I took this photo as soon as I lifted the dipstick level, I didn't allow it to run up/down the dipstick)

I'm pretty sure what's happened here is the place I got it serviced at 2 months ago has put too much oil in, and so the excess oil pressure has forced the oil up into the intake manifold when I was driving it a bit "sportily" at 5000 revs the other day (still not near redline).
What do you guys think?

Anyhow, I rang them up and booked it in ASAP, and they said they'd cover the cost of cleaning it up and getting rid of any excess oil.

 

[scotman]

You are lucky that the oil didn’t get too churned up by the crankshaft. Oil pumps are not very good at pumping air.

 

[92carmnad2]

You are lucky that the oil didn’t get too churned up by the crankshaft. Oil pumps are not very good at pumping air.

Not ruling out anything else is wrong with it as a result of the extra oil. I'm assuming the reason why it's running poorly is just the lack of airflow due to oil in the intake. But maybe it could have fouled the spark plugs as well from the oil being pulled in from the intake? Or if the oil has come up through the PCV valve it could clog the PCV valve?

 

[Handy Andy]

You may have had someone at the last oil change - overfill it.

If it's relatively new fresh oil- the PCV valve sucks it OUT OF the engines crankcase - and into the INTAKE manifold. That is where the throttle body and that snorkel mount to.

Don't go over 4Qts or 3.8L when they add new oil - (with new filter) if you can avoid it, for you get results like that - it will force the motor to try and reburn that oil - it's only supposed to burn fumes from the crankcase - so the oil level - being too high (overfilled) the PCV valve has no choice but to suck in that oil unit the crank oil level drops and it pulls in the foul air not the oil - out of the crankcase.

The PCV gets its power to do that, from the vacuum the Intake manifold provides - so the PCV is a pre-set height in the engine (specific location) so the oil level - if too high, can submerge the PCV valve in oil - so all it does or can do is - done with that oil.

This also happens when the DON'T change the filter at the same oil change - easily enough to make the mistake of overfilling it.

The best way to describe this...so it helps.

In GM and many others - the PCV valve itself - still goes to the manifold for vacuum to get the "foul air" in the crankcase - back into the cylinders to get reburned. But from the TOP of the valve cover - which you get the fresh air in from another way via the valve cover using a Breather - with the air inlet going on the opposite side or opposite cylinder bank..

​

Which, is all well and good, as long as you have clear, or clean passages large enough and not plugged with oil - to vent the same crankcase fumes from the cylinder blow-by that happens on every combustion stroke.

The FORD way of doing it - uses the PCV valve on the CRANKCASE itself. - means its towards the bottom - where the pistons roam and crankshaft rolls - the blow-by gases are the most prevalent here...but then too, is the oil that drains down from the oil drain passages from the upper cylinder head that contains the valve train - it basically rains oil and forms a fog of fumes here...

​

So, the Oil level SHOULD NOT interfere with this design, but this is an Achilles heel of the Sigma motor design - it sucks in oil that if the oil level is left too high can not only flood the cylinders - but foul out the spark plugs and can damage the engine from the PCV valve being unable to pull fumes - it's pulls in oil back into the intake manifold.

Damage? How? By excessive fluid in the combustion chamber - forcing compression ratios to be too great and blow the cylinder head gasket or the piston ring seals - risking damage to the engine.

​

Now that you have all that oil and it's fumes showing up in the snorkel - might want to change out the Air filter and the breather sponge located in the Air box too. The breather sponge fits - snuggles in - to the bottom piece of the airbox - that is where the upper breather hose routes to the fitting there.

So we are on the same page...

The Fiesta Motor from "J" engine of the Sigma line...

It's PCV valve - it is in two pieces, a outer shell which houses the PCV valve itself - and the baffle unit clamshells inside it - these two work to separate the oil from the fumes and let the PCV valve pull just the fumes.

​

I hope you're still reading this...

The oil showing up in the snorkel is pretty extreme - and rough idle means there is still residual effects from the moment this happened. I say moment because when the engine really revs up - if the pressures inside the motor got too much - the baffle could have dislodged, shifting it's position or cracked open. At high rev, the oil spray can really wash the inner sides of the crankcase - so the oil coating is not new, but it's also not a normal thing to happen. Understandably the PCV valve will collect a lot more fumes and oil spray when the revs are up and the motor is whirring along. It is when the amount of it becomes excessive it might indicate another type of damage, that if left to the next oil change - it may be too late to fix by then, it may require engine rebuild.

What am I talking about?

That second piece - the insert that keeps the oil from splashing into and onto the PCV valve and thru it.

When the PCV assembly is mounted - those two pieces are pressed and bolted into the case of the motor - as a sandwich so it only gets access to the insides thru two ports one near the top and one to let the oil it collected - condensed out - drain out and back into the engine to drip back into the oil pan. So it's pretty secure, but the PCV valve is the one that can get plugged or the grommet that seats and forms the vacuum seal along with the bolted seal sides - the PCV valve can get compromised in two ways - the hose kinking and pinching from the excessive pressure of vacuum during a high rev deceleration or the PCV valve in age, can stick in a position that lets in too much fumes from the motor causing a rough idle and a dangerous condition of blowing the engines own oil seals caused by excessive pressures.

Again, an overfilled oil level and a high revving motor are the combination I'm worried that may have hurt your vehicle.

IF that baffle is dislodged or shattered, you have wounded the motor and it may only be a matter of time before you lose it.

Because - if the baffle is cracked or chunks of it has broken and leaving open holes, the baffle lets in too much oil - or air - at any rev speed - the oil will get into and sucked thru the PCV valve - pulling and lowering the oil level until the amount of oil left in the pan is not enough to pump thru the system - the PCV valve sucked it out and blew it out the exhaust and thru the catalyst - which once that is plugged - is far more of an expense to replace the exhaust system on top of the cost of the rebuild due to loss of oil and it's pressure from the motor sucking itself dry.

IF the opposite is true, where the PCV grommet or case has cracked, you can lose oil thru the cracks in the seal it' forms and with no way to reburn those fumes -they collect and exit out any simple port - including the PCV 's own and you can lose oil and run lean thru those conditions.

Now, understand that the 1.25L Petrol is UK and not sold in the USA, so this post was geared more for the USA enthusiast that uses the 1.6L Fiesta using the Sigma line of motor.

The 1.25L is based upon the Zetec (Duratech) approach - although both have a similar root, the refinements are different and the Zetec was phased out as being from a previous generation Ford produced.

Your valve is located on the Block, near the throttle body - with the breather hose line to the top of the valve cover.​

 

[92carmnad2]

You may have had someone at the last oil change - overfill it.

If it's relatively new fresh oil- the PCV valve sucks it OUT OF the engines crankcase - and into the INTAKE manifold. That is where the throttle body and that snorkel mount to.

Don't go over 4Qts or 3.8L when they add new oil - (with new filter) if you can avoid it, for you get results like that - it will force the motor to try and reburn that oil - it's only supposed to burn fumes from the crankcase - so the oil level - being too high (overfilled) the PCV valve has no choice but to suck in that oil unit the crank oil level drops and it pulls in the foul air not the oil - out of the crankcase.

The PCV gets its power to do that, from the vacuum the Intake manifold provides - so the PCV is a pre-set height in the engine (specific location) so the oil level - if too high, can submerge the PCV valve in oil - so all it does or can do is - done with that oil.

This also happens when the DON'T change the filter at the same oil change - easily enough to make the mistake of overfilling it.

The best way to describe this...so it helps.

In GM and many others - the PCV valve itself - still goes to the manifold for vacuum to get the "foul air" in the crankcase - back into the cylinders to get reburned. But from the TOP of the valve cover - which you get the fresh air in from another way via the valve cover using a Breather - with the air inlet going on the opposite side or opposite cylinder bank..

View attachment 8079

View attachment 8081​

Which, is all well and good, as long as you have clear, or clean passages large enough and not plugged with oil - to vent the same crankcase fumes from the cylinder blow-by that happens on every combustion stroke.

The FORD way of doing it - uses the PCV valve on the CRANKCASE itself. - means its towards the bottom - where the pistons roam and crankshaft rolls - the blow-by gases are the most prevalent here...but then too, is the oil that drains down from the oil drain passages from the upper cylinder head that contains the valve train - it basically rains oil and forms a fog of fumes here...

View attachment 8080
​

So, the Oil level SHOULD NOT interfere with this design, but this is an Achilles heel of the Sigma motor design - it sucks in oil that if the oil level is left too high can not only flood the cylinders - but foul out the spark plugs and can damage the engine from the PCV valve being unable to pull fumes - it's pulls in oil back into the intake manifold.

Damage? How? By excessive fluid in the combustion chamber - forcing compression ratios to be too great and blow the cylinder head gasket or the piston ring seals - risking damage to the engine.

View attachment 8082​

Now that you have all that oil and it's fumes showing up in the snorkel - might want to change out the Air filter and the breather sponge located in the Air box too. The breather sponge fits - snuggles in - to the bottom piece of the airbox - that is where the upper breather hose routes to the fitting there.

So we are on the same page...

The Fiesta Motor from "J" engine of the Sigma line...

It's PCV valve - it is in two pieces, a outer shell which houses the PCV valve itself - and the baffle unit clamshells inside it - these two work to separate the oil from the fumes and let the PCV valve pull just the fumes.

View attachment 8085​

I hope you're still reading this...

The oil showing up in the snorkel is pretty extreme - and rough idle means there is still residual effects from the moment this happened. I say moment because when the engine really revs up - if the pressures inside the motor got too much - the baffle could have dislodged, shifting it's position or cracked open. At high rev, the oil spray can really wash the inner sides of the crankcase - so the oil coating is not new, but it's also not a normal thing to happen. Understandably the PCV valve will collect a lot more fumes and oil spray when the revs are up and the motor is whirring along. It is when the amount of it becomes excessive it might indicate another type of damage, that if left to the next oil change - it may be too late to fix by then, it may require engine rebuild.

What am I talking about?

That second piece - the insert that keeps the oil from splashing into and onto the PCV valve and thru it.

When the PCV assembly is mounted - those two pieces are pressed and bolted into the case of the motor - as a sandwich so it only gets access to the insides thru two ports one near the top and one to let the oil it collected - condensed out - drain out and back into the engine to drip back into the oil pan. So it's pretty secure, but the PCV valve is the one that can get plugged or the grommet that seats and forms the vacuum seal along with the bolted seal sides - the PCV valve can get compromised in two ways - the hose kinking and pinching from the excessive pressure of vacuum during a high rev deceleration or the PCV valve in age, can stick in a position that lets in too much fumes from the motor causing a rough idle and a dangerous condition of blowing the engines own oil seals caused by excessive pressures.

Again, an overfilled oil level and a high revving motor are the combination I'm worried that may have hurt your vehicle.

IF that baffle is dislodged or shattered, you have wounded the motor and it may only be a matter of time before you lose it.

Because - if the baffle is cracked or chunks of it has broken and leaving open holes, the baffle lets in too much oil - or air - at any rev speed - the oil will get into and sucked thru the PCV valve - pulling and lowering the oil level until the amount of oil left in the pan is not enough to pump thru the system - the PCV valve sucked it out and blew it out the exhaust and thru the catalyst - which once that is plugged - is far more of an expense to replace the exhaust system on top of the cost of the rebuild due to loss of oil and it's pressure from the motor sucking itself dry.

IF the opposite is true, where the PCV grommet or case has cracked, you can lose oil thru the cracks in the seal it' forms and with no way to reburn those fumes -they collect and exit out any simple port - including the PCV 's own and you can lose oil and run lean thru those conditions.

Now, understand that the 1.25L Petrol is UK and not sold in the USA, so this post was geared more for the USA enthusiast that uses the 1.6L Fiesta using the Sigma line of motor.

The 1.25L is based upon the Zetec (Duratech) approach - although both have a similar root, the refinements are different and the Zetec was phased out as being from a previous generation Ford produced.

View attachment 8087
Your valve is located on the Block, near the throttle body - with the breather hose line to the top of the valve cover.​

Just got the car back from the garage. They checked and cleaned the PCV valve, and drained the excess oil, but they didn't clean the intake because they said it was quite common for Fords to have some oil in the intake. It's running a little rough but it's not as bad as it was. It was that bad before the door was bouncing up and down if I left it open.

I'll do some research into the baffle, see if I can diagnose anything. I asked them to specifically check the PCV because I was worried about seals and the head gasket, but apparently it was in very good condition. I'd also like to check the spark plugs to see if they're fouled at all, but I need to get a spark plug socket and awkwardly it seems spark plug torques fall around the min and max torques of my two torque wrenches, which are both different drive sizes (annoying). My small torque wrench is max 25 Nm and my larger has a min of 27 Nm.

It's strangely still rough at just under 1500 rpm however, which was the same as when I had a misfire in the past, where the misfire would feel the worst at just under 1500 rpm.

 

[Handy Andy]

This is where the concerns is, the idle - did they do any sort of re-learn procedure?

The throttle body being cleaned, might need to have a relearn to set the idle speed and mixture - it's nothing difficult, even you could do it. If you can pull a battery cable from it's post and put it back on bolt it down - yes you can do it.

There are several threads about how to do it, let alone how other from You Tube do it - might want to check those if you have more questions.

https://www.fordfiesta.org/threads/rough-ilde-and-rev-fluctuation.8774/post-23579
https://www.fordfiesta.org/threads/issues-after-water-pump-install.8501/post-22240
https://www.fordfiesta.org/threads/body-control-modual.8227/post-20339

The above should get you thru to a point where you'll be on firmer footing knowing what you're up against.

Ok, to touch base on some other stuff...

The PCV valve - itself - would look clean once it gets bathed in oil - but that means nothing unless it's flushed out and the oil that was in it is removed - best to just replace it with a new one - it's cheap insurance.

Might want to take a moment while the motor runs at idle - so you can get down to the pavement and look up and hear the motor run, any loud clanking may indicate an issue you'll have to sort out.

Go to the rear tailpipe and notice the odor of the exhaust, if it doesn't seem clean you notice soot or smells oily or like a snow blower on a winter day - like it's rich, then the misfire is hiding something else.

Why? Well, the oil sludge the motor has - will work it's way thru finally to the tailpipe, but in the meantime the exhaust system and the catalyst are also affected - this can set a MIL (Check Engine Light) due to the idle running rough. For if it doesn't clean up soon, this can mean more issues for the engine down the road, and they are not good...

Spark plugs can foul out and cause misfires which can easily set the MIL light and also hide other conditions that cause the misfire - including excessive oil. Bringing us back to the PCV valve and the reason for this mess.

Surprised the shop has excuses for this - older car or not, you have an MOT to deal with - it may not pass it if this keeps up.

 

[92carmnad2]

This is where the concerns is, the idle - did they do any sort of re-learn procedure?

The throttle body being cleaned, might need to have a relearn to set the idle speed and mixture - it's nothing difficult, even you could do it. If you can pull a battery cable from it's post and put it back on bolt it down - yes you can do it.

There are several threads about how to do it, let alone how other from You Tube do it - might want to check those if you have more questions.

https://www.fordfiesta.org/threads/rough-ilde-and-rev-fluctuation.8774/post-23579
https://www.fordfiesta.org/threads/issues-after-water-pump-install.8501/post-22240
https://www.fordfiesta.org/threads/body-control-modual.8227/post-20339

The above should get you thru to a point where you'll be on firmer footing knowing what you're up against.

Ok, to touch base on some other stuff...

The PCV valve - itself - would look clean once it gets bathed in oil - but that means nothing unless it's flushed out and the oil that was in it is removed - best to just replace it with a new one - it's cheap insurance.

Might want to take a moment while the motor runs at idle - so you can get down to the pavement and look up and hear the motor run, any loud clanking may indicate an issue you'll have to sort out.

Go to the rear tailpipe and notice the odor of the exhaust, if it doesn't seem clean you notice soot or smells oily or like a snow blower on a winter day - like it's rich, then the misfire is hiding something else.

Why? Well, the oil sludge the motor has - will work it's way thru finally to the tailpipe, but in the meantime the exhaust system and the catalyst are also affected - this can set a MIL (Check Engine Light) due to the idle running rough. For if it doesn't clean up soon, this can mean more issues for the engine down the road, and they are not good...

Spark plugs can foul out and cause misfires which can easily set the MIL light and also hide other conditions that cause the misfire - including excessive oil. Bringing us back to the PCV valve and the reason for this mess.

Surprised the shop has excuses for this - older car or not, you have an MOT to deal with - it may not pass it if this keeps up.

I cleaned the throttle body myself since I did that before I noticed the oil. To do so I disconnected to battery, took the throttle body out to clean it, then put it back in. The time the battery was disconnected for half an hour and I also touched the positive and negative leads together after doing some research into resetting the ECU (the time was reset and so were my radio presets). I then let it idle for about 15 minutes.

As for the PCV valve they told me they had carbon cleaned it including the inside. I've listened to the motor running and can't hear any strange noises. The exhaust smoke is almost a non-existent white that it's always been, not the bluey grey I was expecting when I was checking if it was burning oil. No coolant decrease, not enough smoke and not white enough, and oil looks fine so not worried about coolant leaks. The inside of the exhaust is spotless, there's not even enough carbon/soot to cover my fingertip.

And thank you, I'll have a look at those threads.

Edit: I am tempted to get a new PCV valve as you say just because they're cheap.

 

[Handy Andy]

Wow!

The inside of the exhaust is spotless, there's not even enough carbon/soot to cover my fingertip.

Even after all that.

Ok, then the "glitch" or rough idle can require a going over the motor and making sure they seated and put all the hoses in the right place.

Since you have a 1.25L you have a unique motor that not many have - so the condition is not easily to duplicate on another Ford unless it's similar in engine and type.

So going by "rough idle" below 1500 RPM, that usually indicates a idle air quality issue, there are several hoses and they provide a path for air to get thru that is part of it's budget to make the engine run smoothly when it's at idle.

• You mentioned the throttle body - cleaning it. There is a gasket on the intake to body along with several ports for the EVAP and Brake Booster line (if you have one) and they too can be seen thru the "bore" left when the throttle case is removed.
• To cover your basses (er - bases) the gasket the Throttle body uses, can get gunk in it and you may need to clean that out as well as look into locating a spare throttle body for the older OEM one may have been aging and the teeth used in the cogs of the gears - may have started to wear out generating an out of tolerance problem of slop that idle trim can't quite get right.
• I have taken a star bit to the throttle plate inside my own and "recentered" the plate to the bore - as a clearance adjustment to help it set trim - this may be needed as for cleaning can alter the plate if only by the cleaning effort itself.

When there is enough balance of air "leaking in" thru the EVAP, PCV, and EGR system that the throttle plate then all it has to do is "trim" any richness left from it to smoother idle and fuel trim by setting angle - which is that re-learn process.

 

[92carmnad2]

A month later and still having issues; when warmed up the idle is rough, and it's really rough at just under 1500 rpm, but fine at all other revs.
After doing more research I invested in an OBD2 adapter for FORScan. It seems I have some worrying results for the downstream oxygen sensor?
The downstream oxygen sensor reads a steady high 0.7 while I'm driving however, and I have no rough engine issues whilst driving. When I start the car up the downstream O2 sensor is also stable. It's only once it gets warm and is idling does it behave like this.
I have marked where the engine is roughest (at 1500 rpm). The throttle position alternates between 12.94% and 13.33%, and you can see the revs oscillating with it - which translates to added roughness it feels.
Edit: could it be a vacuum leak?

 

[92carmnad2]

Did a scan today and the O2 sensor 2 seemed to be fine all the way throughout, not sure why it went so low in the previous scan?
Anyhow, going off the oscillation of the revs in the previous scan I sent, I did another just about where the roughness begins, which is at about 1300 rpm. I held the throttle as steadily as I could, and you can see the oscillations. The frequency of the stalling-like jerkiness I feel matches up exactly with the fluctuations in RPM.

 

[Handy Andy]

You are definitely showing something happening in the O2 side. Bank 1 Down stream.

Yours a manual or Auto?

The lag looks excessive - that slope is what I referring to

Since that tracks output mixing in with outside air, this may be a plugged catalyst or a exhaust manifold leak, but have to rule out simple stuff first - Autos have EGR so EGR ok?

Thanks for bringing that FORScan tool along, they're pretty powerful - thanks for sharing the diagnostics.

 

[92carmnad2]

You are definitely showing something happening in the O2 side. Bank 1 Down stream.

Yours a manual or Auto?

The lag looks excesive - that slope is what I referring to

Since that tracks output mixing in with outside air, this may be a plugged catalyst or a exhaust manifold leak, but have to rule out simple stuff first - Autos have EGR so EGR ok?

It's a manual. I've looked at the symptoms of a plugged catalyst but I've got no issues at higher RPMs like the videos I've watched seem to display.

 

[Handy Andy]

Ok, then it's a transition from "idle" to off-idle being drive.

I've looked at the symptoms of a plugged catalyst but I've got no issues at higher RPMs

That's correct. There would be a longer slope, and since you have a Manual, in the USA we don't need EGR for Manual, cannot guarantee that for UK/EU Countries - but less complexity forces us to see the issue for more of an intake side problem.

But that slope is showing us a long-term - "digestion" - of slow recovery of exhaust possibly from oil consumption the engine is poofing (Puffing) through.

 

[92carmnad2]

Ok, then it's a transition from "idle" to off-idle being drive.


That's correct. There would be a longer slope, and since you have a Manual, in the USA we don't need EGR for Manual, cannot guarantee that for UK/EU Countries - but less complexity forces us to see the issue for more of an intake side problem.

But that slope is showing us a long-term - "digestion" - of slow recovery of exhaust possibly from oil consumption the engine is poofing (Puffing) through.

The fact I can't seem to find any EGR valves online for my year and engine, tells me that it doesn't have an EGR valve. I can only find them for the diesel model of my car.
If I had oil consumption wouldn't I be seeing some side effects from the exhaust smoke?

 

[Handy Andy]

Reviewing some more and working with what I know, the issue of the vacuum leak - versus more of a timing issue - comes in.

Have you got access to a vacuum gauge? The sensor as the MAFT (Mass Air Flow and Temp) got put in below the throttle plate on later models (2014 revision forward) - but on yours it's still in the air snorkel ABOVE the throttle. So it can't see the vacuum directly as it is a programmed "advance" which is why the above statement has to be said, for we go down a rabbit hole that many wouldn't like to, let alone understand for the realm of the timing advance comes into play here.

So for that much oil to show up - tells me a cracked/warped head, Piston Ring - or bad valve seal or some form of a catastrophic event took place, the only evidence we have is the oil sludge, the transition of idle to off-idle roughness and the subsequent performance dies as a result.

The only thing you have not mentioned is how the upper air line is for purging the foul air inside the crankcase is doing.

Pull that and see if a vacuum can form - work the idle speed up slowly until this sputtering occurs - if more smoke or fumes start to leave the upper vent - then the issues of blown rings comes in as in the reason for the oil was (possibly but clues need to fall into place - not off the hook-yet) not due to overfill, but as a fail and eruption of oil into the crankcase caused by excessive blowby of combustion - that is occurring in off-idle as the revs go up.

Check coolant for dark fluid - A possible blown head gasket and the check with a compression test is then in order.

Another scenario is the failure of one of the advance solenoids, which may mean more of a sealing issue affecting a timing one, the two cam sensors themselves would set off a light if they saw erratic behavior - so it's not showing up excessively yet. At least by the Check Engine light.

As the engine warms up - look for operation of the coolant tank, loosen the cap and observe this sputtering - see if air bubbles form going up into the tank, during this idle to off-idle transition - then this indicates as the idle revs up the gasket can't contain the combustion - the system has a warped or blown gasket (potentially).

IF the Coolant seems to stay clean then rings being below the gasket seal - means the blowby is forced below - so that usually tells me rings.

 

[92carmnad2]

Check coolant for dark fluid - A possible blown head gasket and the check with a compression test is then in order.

IF the Coolant seems to stay clean then rings being below the gasket seal - means the blowby is forced below - so that usually tells me rings.

Thank you for your reply, I have checked the oil and the coolant and both seem perfectly fine, and the level of coolant has never changed (apart from when heated up of course). Taking the top off the coolant reservoir also reveals no bubbles at all. The exhaust smoke is non-existent, apart from pale white at acceleration once warmed (otherwise it's spitting water from condensation).
I have also taken the spark plugs out, and all seems fine to me (yes I finally got the correct size spark plug socket). These ones are only just over 3 months old. It seems that in the past, however, that the previous owner maybe had an oil leak in the spark plug wells? Also, if it was piston rings wouldn't I be seeing oil on the piston head in the second photo, or would it be isolated around the edges of the piston head?

Have you got access to a vacuum gauge? The sensor as the MAFT (Mass Air Flow and Temp) got put in below the throttle plate on later models (2014 revision forward) - but on yours it's still in the air snorkel ABOVE the throttle.

I haven't got a vacuum gauge, also, isn't it just the MAP and temperature sensor in this model of Fiesta? A friend of mine who's a mechanic seemed to think it had a MAF sensor as well, since they recommended giving it a clean, but I don't appear to have one.

I have also recorded a video of the sucking noise it makes when applying the throttle. I haven't mentioned this so far because I'm not sure if this is normal or not, but I don't ever recall this noise happening before my issues started, it was at least not as prevalent anyway. It also makes the same sucking/hiss abruptly when the engine shuts off. The shaking of the engine is stabilised by my phone's camera, and there's no way to disable it on my phone (I've tried). You can still see the sudden jerk of the air intake pipe however.
https://youtube.com/shorts/dNueW_kISrI?feature=share
(I live next to an airport).

The only thing you have not mentioned is how the upper air line is for purging the foul air inside the crankcase is doing.

Pull that and see if a vacuum can form - work the idle speed up slowly until this sputtering occurs - if more smoke or fumes start to leave the upper vent - then the issues of blown rings comes in as in the reason for the oil was (possibly but clues need to fall into place - not off the hook-yet) not due to overfill, but as a fail and eruption of oil into the crankcase caused by excessive blowby of combustion - that is occurring in off-idle as the revs go up.

Do you mean for the purge valve or the crankcase breather? I tried to see if I could get the pipe off the purge valve to see if it was pulling air through, but it wouldn't budge. I disconnected the purge valve while the engine was running as well to see if it had any effect, and it didn't, and didn't throw an engine light either, which I was expecting it to.

Edit: it might be useful actually if I uploaded a video of how it behaves at 1500 rpm, where the engine roughness becomes really noticeable.

 

[Handy Andy]

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Aside from some dirt in the seating - the top of the piston appears normal and I's thought we'd see more "threads" in this photo but as far as I can tell aside from the dirt - which can cause a condition of a vacuum leak thru the spark plugs threads...I see little (READ none) evidence to bolster the argument of ring issues either - so we can push that aside - good work on this documentation effort...

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What plugs are these?

It's this photo that struck me, because the Electrodes and the insulator are VERY clean - the only fouling evidence is at the cooler portion of the plug - that being the threads - which carry the heat away. So I see not too much out of the ordinary except for the dirt in the "Seat" of the plug on the head - wondering if the vacuum leak is something that is what is causing this.

Ok to help the issue of the "PCV foul air" purge line - that clip - the one on the cover is a "pinch to clip retracted" where you pinch the two tangs to meet in the middle and they will clip together (you'll see the "hole that tab meets up with and you pinch it) and stay in place to help remove the hose from it's fitting or let you reposition the clip off the nose of the hose - then when completed, you can pry it off that hole in the clip - both tabs will snap it pinching to the hose in place (Spring steel action). - the other fitting on the air box, that airbox one is a pry up - you "lift it off" by using two wide flat blade screwdrivers to put their flats on the flare of the outer sleeve, and simply and gently - pry up - with "up" being to pop it off the valve stem it's press fitted onto - vertical off it's surface - not up towards you just up from the pinch point - you can see this action at those clips pop off the flange or flare of the stem on the Airbox side.

To help, I find removing the hose side, at the valve cover, is more effective in finding the foul air - if it smoke comes out - the PCV valve is being overwhelmed - you might want to keep the hose off as you rev the motor to this 1500RPM limit and above - if more smoke comes out - then the problem is a ring leak or poor seal somewhere, this will have to be fixed soon, else it can blow seals and then you'll need even more money to service the oil puddles this thing can leave behind.

When I say overwhelmed - the PCV valve can only take in so much blowby the rest flows out to the snorkel and re-caught in the air filter before it is taken back in at the throttle body. This oil sludge can affect the MAF performance so it might be in order to inspect the Air Filter and Air box (the carriage that holds the filter) for oil sludge collection - if a lot of oil is in there you'll have to clean it out, the MAF will need a cleaning and the Air Filter if not already done - replaced too.

The MAF sensor, you may have one on the Airbox (air filter housing) on the plastic nozzle to the throttle body. - That fitting can also need cleaning - as well . I did not see it in your photos of earlier so I thought the older MAF only system and the MAFT were combined at the intake - not two separate spots,

The graphic though, kinda leans me towards a "spent" Catalyst or plugged one, the recovery lag is showing, yes, but those slopes or waves that start out small - then recover to their normal amplitude, is what tells me the efficiency is dropping but from exhaust gasket leak or intake fault or some other exotic event letting it see air and not recover as quickly is what gets me.

The PCV is not totally ruled out for air can leak in thru the housing if you have this much oil, in the snorkel, something blew - and that can mean the PCV seal it has to the engine block (it's bolted to the side of the motor behind and under the intake) - are those seals are damaged?

This "foul air" test as well as vacuum leak test - can rule out these in one way or another. If you can';t develop vacuum in the hose or fitting by placing your thumb over that hole and wait for vacuum, if it can't do that, then suspect seals are getting ready to fail because the PCV valve is not pullnig enough to generate a vacuum to purge the foul air out and let fresh air in.

 

[92carmnad2]

To help, I find removing the hose side, at the valve cover, is more effective in finding the foul air - if it smoke comes out - the PCV valve is being overwhelmed

You'll have to forgive me, I'm not very familiar with these tests. Do you mean take the hose off of the PCV valve itself, and watch if the PCV valve is emitting smoke?
My PCV valve configuration is like this.

Ok to help the issue of the "PCV foul air" purge line - that clip - the one on the cover is a "pinch to clip retracted"

I think I was thinking you meant the EVAP purge valve originally. I was referring to the pipe below. I wanted to see how the EVAP purge valve was operating, but the pipe itself is incredibly stuck on - there was no issue with the clip.

 

[Handy Andy]

Er no, the one I'm referring to in the one that heads to the Air box,

There is an easier way than that.

Leave the EVAP alone for now, that may be an issue if the Idle to Off-Idle mixture is being caused by a lean condition - due to a plugged evap line - that is possbile too. Oil in the Intake, this EVAP hose goes into the Intake too.

But we need to know if the PCV valve is able to suck air into the crankcase nearly all the time for it to work correctly and prevent the oil seeping into the Intake.

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Just unscrew those bolts off the top of the airbox, loosen the cover so you can view the Air filter and below it, on the Airbox itself, where the Air filter rests, is the PCV foul air inlet to the upper hose on the valve cover. It's clipped to the side of it.

Start the car, remove the cover and the Air filter and see if you have a plugged PCV breather line or there's a bunch of gunk in it preventing it from letting air in.

Good time to check the Air Filter too, make sure it's not coated in oil either...

The PCV breather hose needs to be free of oil and debris, that is it's purpose - to breathe, let pressure equalize - else it can't balance the air pressures inside the motor - seals can fail due to that.

When you open the Air box, look in the spot where that hose I point to - in the above photo, goes into - there is an opening and the housing holds what looks like a sponge - that is the filter element the PCV uses to gather up and filter out the heavier particles and oil in the vapors from the crankcase and purge foul air using the Air box to do this.

Once you can see the PCV vent in the airbox, make sure you can feel air moving into this vent area in the airbox, if it's plugged, this may be part of the problem - oil backed up into it and plugged the line with the sludge it can leave in the line over time from such an similar event.

Then shut off the motor - reassemble everything back ,and let us know what you find.