Need Help! 2017 S3 - Burbling/Stuttering Idle once the car has warmed up

[Jacob Lever]

Hey guys, apologies if there is already a thread for this, but from my searches I haven't found anything exactly the same as my issue.

Some background: my S3 is completely stock other than a resonator delete, I recently changed the spark plugs 10-15K Kms ago, and oil+filter change <5K Kms ago.

My problem: So to put it simply my car has a burbly/stuttering idle when the car has warmed up and I stop at a red light or even when in park. The car drives perfectly fine otherwise no noticable changes in performance or smoothness when moving. I have attached a video as this issue is pretty hard to describe obviously lol. The engine does seems to shake more aggressively in sync with the exhaust stuttering and has a bit of a constant shake but nothing super concerning. Oh also there is not change in the RPM so I'm pretty stumped as to what the hell is going on here.

I have checked my PCV, as I heard that it can cause similar rough idle if the vacuum seal is broken, but it seems to be fine as there is no pressure when I place my finger over the hole. I have also ruled out the spark plugs as I changed those very recently and they are just the OEM spec spark plugs, but I will take them out once it warms up in my area and visually check them.
I have OBD11 but I am not getting any faults that I believe would cause this, but I will attach some screenshots incase I am wrong. I do not have a check engine light either all my faults are intermittent.

I would also like to note that the stuttering has seemed to gotten more frequent over time(or maybe I just notice it more now) but they aren't exactly changing or getting more aggressive. In the cold weather they seem more prominent but that could just be me.

Any help with this would be great!

Thanks,
Jacob.


VIDEOS:
https://youtube.com/shorts/c1LPELbpS5s?feature=share
https://youtube.com/shorts/k5QkUMEnXYE?feature=share
https://youtube.com/shorts/NYowCszmLFM?feature=share

Fault Codes:
Attachment 323582Attachment 323583Attachment 323584

[o1turbo30v]

injector dieing or you need carbon cleaning would be my guess, you can send an oil sample into Blackstone and they can tell you the amount of fuel dilution in the oil. You do have a fault code for your exhaust valve motor but itd be very surprised that would cause an issue like you are describing.

[Jacob Lever]

injector dieing or you need carbon cleaning would be my guess, you can send an oil sample into Blackstone and they can tell you the amount of fuel dilution in the oil. You do have a fault code for your exhaust valve motor but itd be very surprised that would cause an issue like you are describing.

The injectors probably have never been replaced on this car I'm at ~76,000 Kms right now, so I'll get those ordered in ASAP as it's probably a safe bet. I'll look into the carbon cleaning if the injectors don't fix the issue. For the exhaust valve motor I would be surprised too as I'm 90% sure that one of the motors just froze up a couple weeks back when it was getting into the mid -30 C. I did give them a visual check and they seem to be functioning properly now.

I'll update once I get the injectors replaced, I'm praying that will fix this issue

[Jacob Lever]

Oh I see, thanks for that extra info! I don't have the tools to do a professional carbon cleaning, but if I notice a lot of buildup I may just do a DIY cleaning with the zip tie method I have seen on Youtube that should do the trick for my purposes.

Just curious about how many Kms did you have on your car when you changed your injectors(if you changed them)?

Thanks!

[ReggieNoble]

Oh I see, thanks for that extra info! I don't have the tools to do a professional carbon cleaning, but if I notice a lot of buildup I may just do a DIY cleaning with the zip tie method I have seen on Youtube that should do the trick for my purposes.

Just curious about how many Kms did you have on your car when you changed your injectors(if you changed them)?

Thanks!

Replace both your map sensors, I bet it fixes it. Dirty injectors will give you problems at idle and under load

[Jacob Lever]

Replace both your map sensors, I bet it fixes it. Dirty injectors will give you problems at idle and under load

I could try this first since the install is a lot easier, but what makes you say this, have you had this problem before?

Also I was trying to find the locations for the MAP sensors and I found this Integrated Engineering installation guide for their tuned MAP sensors, just want to confirm that these instructions would probably be the same for just replacing with stock ones: https://cdn.performancebyie.com/guid...20-IEELCI5.pdf

[Jacob Lever]

My 2015 S3 has 297728km. Its on its 3rd set of injector. Plus a new engine. I DIY all its maintenance. I have previoisly posted here an injector and carbon job.

Thanks! I found some pretty comprehensive youtube video that should be enough for me, I am generally pretty handy, just don't have all the same tools as the professionals.

[S3DAN]

Replace both your map sensors, I bet it fixes it. Dirty injectors will give you problems at idle and under load

I agree this is the most likely culprit. Replace both the upstream and downstream o2 sensors and all your problems will go away. Check around for sensors and you can use an aftermarket just check the warranty details and brand (look for german/hungarian) .

One sensor is on either side of the turbo pretty much and you can even rent the specialty socket like I did. I changed out both o2's, spark plugs, and PCV valve and it cleared up all my misfires. I didnt do all 3 repairs at once. In my case I always kept fresh plugs (like you) but always had a nagging idle misfire and an increasingly annoying misfire under light load but with fresh plugs/coils i knew it wasnt that.
The main culprit ended up being the "up stream" sensor which is on the cold side of the turbo causing the most issues. Carbon cleaning and injectors are usually the first recommended thing and usually the last thing that needs to be done in reality. Sorry but in a turbocharged and pressurized system a little junk on a valve isnt a big deal unless the gunk were causing your valves to not seal (casuing a pressure leak) which is very unlikely.

TL;DR your o2 sensors are torched brah

[ReggieNoble]

I could try this first since the install is a lot easier, but what makes you say this, have you had this problem before?

Also I was trying to find the locations for the MAP sensors and I found this Integrated Engineering installation guide for their tuned MAP sensors, just want to confirm that these instructions would probably be the same for just replacing with stock ones: https://cdn.performancebyie.com/guid...20-IEELCI5.pdf

Top of intake manifold and throttle body pipe, they get residue in them over time (just like the intake manifold and ports/runners). A bad pcv is usually what starts all the issues. Pull the one on the top of the intake manifold just to check. I bet it's almost clogged up with oil residue.

[Jacob Lever]

Top of intake manifold and throttle body pipe, they get residue in them over time (just like the intake manifold and ports/runners). A bad pcv is usually what starts all the issues. Pull the one on the top of the intake manifold just to check. I bet it's almost clogged up with oil residue.

I went ahead I pulled out the MAP sensor on the intake manifold and I've included some pictures for you to see. From what I can tell it looks not too bad, a little bit of oil but nothing major. I did clean it off with some MAF sensor cleaning spray I had laying around helped make it look a bit cleaner, I went for a little ride around and the idle stuttering was still happening so cleaning it didn't do much.

I did notice some oil residue around the PCV valve and it make me want to replace it, but I'm not too sure. I have also attached some pictures of that as well.
Attachment 323698Attachment 323699Attachment 323700Attachment 323701Attachment 323702

[Jacob Lever]

I agree this is the most likely culprit. Replace both the upstream and downstream o2 sensors and all your problems will go away. Check around for sensors and you can use an aftermarket just check the warranty details and brand (look for german/hungarian) .

One sensor is on either side of the turbo pretty much and you can even rent the specialty socket like I did. I changed out both o2's, spark plugs, and PCV valve and it cleared up all my misfires. I didnt do all 3 repairs at once. In my case I always kept fresh plugs (like you) but always had a nagging idle misfire and an increasingly annoying misfire under light load but with fresh plugs/coils i knew it wasnt that.
The main culprit ended up being the "up stream" sensor which is on the cold side of the turbo causing the most issues. Carbon cleaning and injectors are usually the first recommended thing and usually the last thing that needs to be done in reality. Sorry but in a turbocharged and pressurized system a little junk on a valve isnt a big deal unless the gunk were causing your valves to not seal (casuing a pressure leak) which is very unlikely.

TL;DR your o2 sensors are torched brah

I'm not getting any idle misfire codes or any drivability issues whatsoever, I'm just curious was your idle somewhat similar to mine maybe more aggressive and rough since it was actually misfiring? I'm just trying to narrow down end result here because my symptoms are probably early signs of something like misfiring.

[ReggieNoble]

I went ahead I pulled out the MAP sensor on the intake manifold and I've included some pictures for you to see. From what I can tell it looks not too bad, a little bit of oil but nothing major. I did clean it off with some MAF sensor cleaning spray I had laying around helped make it look a bit cleaner, I went for a little ride around and the idle stuttering was still happening so cleaning it didn't do much.

I did notice some oil residue around the PCV valve and it make me want to replace it, but I'm not too sure. I have also attached some pictures of that as well.
Attachment 323698Attachment 323699Attachment 323700Attachment 323701Attachment 323702

If you haven't figured this out yet, I would also look into the cam adjuster magnets, they too can cause those symptoms, usually accompanied with hard hot starts, without a dtc.

[Jacob Lever]

Yeah I haven't figured it out yet, I'm taking it to one of my local Audi mechanics soon to get a professional diagnosis on the issue. I don't think it is the cam adjuster magnets as I have no problems starting at all, whether it be in the cold or in the heat she starts and runs great.

[Jacob Lever]

Hey guys just got an update on the situation,

So I was playing around on OBD11 and figured out I can view the live data for the engine, including the #of misfires on each cylinder (Modules->Live Data->"Numb.of misfir., cylinder {#}").
I could then see that cylinder 3 was having considerably more misfires while idling and incremented synchronously with the engine stutters. See below...
Attachment 324776

So to distinguish between the coil pack and the spark plug I first moved the coil packs around, but there was no change(coil packs seem fine).

I then moved spark plug #3 to cylinder #2 and this is the results...
Attachment 324775

As you can see the spark plug went bad. But the strange thing is that I had just replaced these <15,000 Kms ago so I ruled them out first.

So I did a bit of research and from what I found it is possible that a bad fuel injector can cause the spark plug to go bad, I also have included some pictures of the old spark plugs for reference.
To further back up my theory that the fuel injectors are going bad is this screenshot after I replaced all four spark plugs...
Attachment 324777
As we can see I am still getting 0-5 misfires across all 4, and I noticed that they only popped up when the car was under load(accelerating faster) or interestingly enough sometimes when downshifting in sport mode.

So all of this leaves me to believe that the injectors going bad causing to the spark plugs to fail(worse in cylinder 3), so I will probably get the injectors replaced soon so I don't have to worry about my new spark plugs going bad prematurely.

On a different note I could have just gotten unlucky with one of the spark plugs, but the existence of a couple misfires under load makes me doubt this.

The following pictures are of the old spark plugs labelled for each cylinder, from what I can tell they all look the same wear but if anyone disagrees I'm open to hear what yall think.
Attachment 324780Attachment 324781Attachment 324782Attachment 324783


But overall the idling issue has been solved! I will update in the future on any other things that come up but hope this helps someone!

[ReggieNoble]

Those gaps look quite large, what are they set at?

[Rod Paine]

Yes, exsevily large! What are they set at?

[Jacob Lever]

I didn't set them just assumed they were the proper gap as I bought them from the dealership, I also don't have a gapping tool. The new ones I put in I didn't gap either but they are not from the dealership they are NGK N94833, do I need to take them out and gap them?

[texasboy21]

Really great catch! Our injectors are definitely on the 'regular maintenance' schedule for higher milage S3s, and Audi has gone through several revisions so make sure you get the newest flavor.