Bad engine vibrations in first and second gear when engine is cold

[zhaniaudi]

I searched the forum and got some clues but would like some more feedback on the following problem for my Q25 B7 S4 (manual):

* Bad engine vibration in first and second gear after about a minute or two of driving (starting from cold engine).
* Lack of power when attempting to accelerate quickly in these gears.
* When engine warms up, vibration issue goes away and car accelerates fine in all gears, no loss of power.
* No check engine light.
* When car is idling, it feels as if there's a misfire now and again (but it can't be since this would produce a code I assume).

Any ideas?

[JimmyBones]

Do you still have the stock catalytic converters?

A lot of the pre-cats clog up and cause the engine to run rough, vibrate, and have a lack of power. I could see your pre-cats starting to fail and not throw a check engine light if you just noticed this. It takes so many misfires in a time period or the cats to fail the warm up efficiency test before the ECU throws a code.

Also the secondary air injection runs the first few minutes of cold start up too. You could have a vacuum leak that seals up once things warm up but I would start by checking the cats.

Do you have a vagcom? If so then do a few things. Like check for intermittent fault codes. Then at cold start up idle and while driving with a cold engine have someone else watch measuring value blocks 15-17 for misfires.

[zhaniaudi]

Do you still have the stock catalytic converters?

A lot of the pre-cats clog up and cause the engine to run rough, vibrate, and have a lack of power. I could see your pre-cats starting to fail and not throw a check engine light if you just noticed this. It takes so many misfires in a time period or the cats to fail the warm up efficiency test before the ECU throws a code.

Also the secondary air injection runs the first few minutes of cold start up too. You could have a vacuum leak that seals up once things warm up but I would start by checking the cats.

Do you have a vagcom? If so then do a few things. Like check for intermittent fault codes. Then at cold start up idle and while driving with a cold engine have someone else watch measuring value blocks 15-17 for misfires.

Stock cats. Rest of the car is stock too. 64k miles on the clock, two (somewhat) careful/sensible owners.

No vagcom but the car is sitting at the local Audi dealer and one of their techs is going to drive it home tonight and back to work tomorrow and see if they can reproduce the issue.

Thanks for the tips.

[zhaniaudi]

Dealer reports intermittent misfires for pistons 7 and 8, most likely due to bad seating of coils.

[zhaniaudi]

Some additional info: It appeared that one of the spark plugs was bad also (piston 8), even though it had just been replaced 3 months ago as part of the 55k service. The dealer replaced this free of charge and also installed two new coils (parts cost only, no labor). Car seems to be running as normal now.

[ladiesgod]

How do you check if your cats are bad?