If only at cold start, it can be linked to some humidity in the connector / wire… Have you inspected the cylinder with a camera to see the walls ? It shouldn’t be that due to your good compressions, but it should not hurt to check.
Haven’t done that yet but usually bad cylinder walls often come with metallic scraping, excessive oil consumption etc. Which I don’t have at all. Considered that theory with my mechanic as well but this would’ve meant that EVERY cold start would be bad right? It’s always just one or two days within a three week interval.
And (this is by far not a scientific study) by my own experience these damages start between 20k and 70k miles usually. Often due to owners neglecting oil change intervals and ignoring driving it in. But mine according to audi has been well maintained and is way past that threshold.
I recently had a similar problem with random misfires. For me, the problem seemed to disappear after:
- replaced the electrical connector to the throttle body (I had a bad crimp on one wire), and/or
- re-charged/replaced the battery (see: Phantom power drain and MOST optical bus issue)
Thank you I will try that! I’ve had multiple occasions where the battery light would flicker for a second 90% of the time it misfired.
UPDATE: checked the sparkplug and it looked very good, not even remotely caked up. Issue kinda feels like a having MAF problem (RPM going up and down) also I’m having an appointment for an endoscopy next week which hopefully does not reveal something bad.
But the typical symptoms are not shown:
-no excessive oil consumption
-no loss in compression
- sparkplug in good shape and condition
Any other things you guys recommend checking in the meantime? Gonna use all your advice this weekend!
I have some misfires. My theory is that I have an air leak.
When I cranked down on the IM bolts I could reach, the frequency seemed to lower. I cannot reach the ones under the throttle body without pulling it, and I believe I still may have an air leak in the throttle body/plenum area that may be contributing to it.
I haven’t had a chance to prove this, but the misfires are not causing any performance issues, since like you, they go away when warm and fortunately when cold, they are minor.
Maybe you can use a smoke stick to see if any is being drawn in around the IM or Throttle plenum areas.
Ed
My original IM developed leaks at all 4 corners. We discovered it by pressurizing the IM and applying a soapy solution to the exterior of the IM. Unfortunately, that required replacement.
Just to follow up—misfires came back. So the battery is not the only problem
Is it during cold starts only or also during driving? Have you done an endoscopy of the cylinder walls?
It’s just random/occasional misfires at idle. Mostly happens in bank2. I swapped a coil pack between banks and the faults did not move.
If I reset the codes while the engine is warm, I can drive aggressively for hours (2lane mountain passes) and the engine is perfect.
Does the CEL flash? How are the misfires felt? Like aggressively or just a slight tickling? If it’s a tickling it might be a leak within the PCV system.
But before you go ahead and starting buying parts and changing them I’d take a look at the cylinder walls nevertheless. I looked at mine and saw the alusil coating peeling off on all cylinders which is the fate of every FSI V-engine. Seen 3.2s and 4.2s doing it too.
When it misfires, It’s usually just a rough idle with the CEL flashing.
Also, I recently replaced the oil separator and that seemed to fix the occasional P0171/0174 system too lean codes. But I did note that the membrane of the old part was still intact.
Did you check the hose for any cracks?
What about the timing on bank 2?
Oily coil pack tips?
At first I’d check the compression ratio on bank 2 and use a camera to get a picture of the cylinder walls. Don’t be like me chasing a problem and spending 11k euros before doing that. It can safe time and money!
Other than that it might be the injectors leaking. Yes they fail a lot and I’d replace all 10 of them at once. If one fails the 9 Other ones will fail shortly after that.
I’ll do that and report back. What is the fix for peeling cyl liners?
Unfortunately a new engine or at least a new block with pistons and heads. I mean that would be the worst case and let’s not hope that it is the case but better be safe and check it too. An overhauled good engine with installation costs around 6k here in Germany or get a used one but always ask for photos of the cylinders and compression stats.
Here are some pics, but i don’t really know what to look for. However, the spark plugs don’t look great. They were last changed in 2016, 40K km ago.
Cyl 6
Cyl 7
Cyl 2 - does NOT misfire
We need to go deeper into the cylinder to see possible damage however 40k km is way too much for these spark plugs in my experience. I’d try changing them and maybe the misfires are gone. Since they already look that bad I’d start with that.