Howdy. New member here. I apologize in advance for the following lengthy explanation. Ill throw a tldr at the end if this is too long.

I have a 06 8p A3 sportback with the 2.0 FSI engine sitting about 144k. I am having a cold start misfire issue in cylinder 3. Let me run over what all Ive done so far. I have dug through the archives on both here and 1 or 2 other audi forums regarding this topic for almost 5 months and now I am almost out of ideas so I figured I would make an account and try to address my issue specifically to see if anyone else had ever found a solution since most forum posts end with OP never following up.

So, I have had this car for about 3 years, well maintained as I am a stickler for keeping that CEL off. But about a year ago it started throwing the CEL for only cylinder 3 misfire. No randoms, no other cyl, only 3 and only in the first 9 to 12 seconds of running after a cold start.

I cant physically really hear/feel the misfire and it only seldom triggers CEL now although it will store a pending code almost every week.

So far I have done the following (via advice on this and other forums):

New coil packs (bosch red)

New spark plugs (NGK gapped at .028)

Full carbon clean of intake valves and manifold (walnut blasted, then finished off with CRC to break loose any deposits left in the cast intake porting)

New intake manifold gasket

New injector seals

New fuel filter (bosch)

New evap purge valve

New pcv valve and breather hoses

Inspected coil wire harness

Found cracked brake booster hose. Replaced hose and valve 4 days ago. (This finally stopped light from triggering daily and zero pending codes for 4 days but I just now got a pending code for cyl 3 misfire yet again an hour ago)

New hpfp follower and seal

New air filter.

Only run premium 91 fuel (highest here) and just ran bottle of BG 44k through last tank then replaced fuel filter.

New valve cover gasket

New belt and tensioner (not related but figure I would throw that in)

Compression test. Results as follows (1-4)

165 165 175 165 (175 is the misfiring cyl) consistent for 144k IMO.


I am suspecting the compression increase in 3 is due to carbon buildup inside the cylinder likely due from a faulty injector not spraying correctly to keep carbon "washed" out.

I will add this. The misfire CEL was being tripped every time I started the vehicle cold 3 months ago but as I researched forum posts and slowly replaced all this stuff, it gradually decreased in frequency to where now, I have only recieved pending codes on every 10th or so cold start but nothing so far has been stored or tripped the CEL (in last week or two, especially after replacing the cracked brake booster hose, and this last week we have been sub freezing every morning)

I am guessing it is either a bad fuel injector or, unlikely, a vacuum leak. Car boosts fine and IMO a vacuum leak should cause random or non cylinder specific misfires and would probably trigger a bank lean code.

I do not own a VagCom reader because this car was not my primary vehicle until recently and I didnt have any plans on doing any tuning or modifications, although it looks like I will be buying one now.

I wanted to get opinions on if this is most likely an injector issue before I go investing more money into parts.

I have read dozens of threads about this and most end up with owner chasing their tail while mechanics and stealership keep misdiagnosing and never figuring out the real reason.


Again, I am really sorry for the long winded post. This will likely be my one and only post on here so bear with me. I am fairly competent with vehicles but this one has me stumped.


Thanks guys.


Tldr: cyl 3 cold start misfire, replaced everything audi forums suggested: carbon cleaned, new coils, plugs, fuel filter, follower, pcv valve, bg 44k treatment, good compression, no visible vacuum leaks but misfire is still there, just less frequent. Bad injector perhaps?

 

My idle is perfect, no hiccups or roughness. Acceleration is perfect as well, no stalling or bucking. And no other check engine lights have ever occurred in last 3 years except when one of my old coils went out 2.5 years ago and I replaced them all with densos (using bosch now) and never had a light again until this problem started.