Stumped on rough 2.7t engine - not coils or ICM I think
 

Hi all,

I'm a long time reader, first time poster. These forums have helped me so many times with my 2000 A6 2.7T 6MT and I first wanted to say that I appreciate all your help!

I'm stumped on a rough engine. I'm getting two codes: for misfire on cylinder 1 and the "random cylinder misfire". I replaced cylinder 1 with a good coil and no change. I replaced every other coil with a good one and there was no change.

I then tried unpluging each coil (1 through 6), one at a time, and each time there was no change to the rough idle (no better and no worse). I thought this was weird...

I then tried unplugging coils 2 and 3 at the same time, and the idle was rougher. I unplugged coils 5 and 6 at the same time, and the engine was just as rough as when coils 2 and 3 were unplugged...

I'm ruling out the ignition control module since two unplugged coils in the same bank was worse than one unplugged coil (my understanding is that the whole bank would be inactive if the ICM was bad, so two coils shouldn't make a difference). It's also not the MAF, since it makes no difference when it is unplugged.

So, I'm stumped. I'm not sure what else it could be. Both exhaust pipes smell of strong gasoline. There's very little power on the road. I should also add that the rough engine was sudden (shut off a well-running engine, got a haircut, and 30mins later it was rough on startup).

Any ideas?

Did you check plugs to make sure they're not fouled. Also no oil in boot cavity?
If I remember correctly you can swap plugs to the ICM (mounted on or near airbox) if you wanted to test.
Random cylinder missfire indicates it's more than just #1. Do you have vagcom?

I would try swapping your ICMs and see what happens. If it follows the ICM, then you have found your problem, if not, then it's back to the drawing board.

The 2.7T is not a fun one to work on, but when it runs right it's fun to drive! Welcome to the club of us 2.7T owners.

Hi all,

Quick update: I was tooling around with Vagcom and discovered the measuring blocks for misfires for each cylinder. I could see that cylinder 1 was misfiring constantly (400 misfires a minute) while the other cylinders were fine. I swapped the ICMs as suggested, and saw the misfire move to cylinder 4, with cylinder 1 being fine. So I bought a used ICM (will arrive in a week) and hopefully this cures it!

I'm glad I found those measuring blocks, as the check engine light codes themselves weren't that helpful. The prior time I swapped the ICMs, I didn't get a code for cylinder 4 misfire, just the generic "multiple cylinder misfire" code.

Also, I had always thought that a failed ICM would cause the whole bank to misfire. I didn't realize that a failed ICM could cause only one specific cylinder to misfire, hence my earlier misdiagnosis.

But, we'll see. I'll let you guys know if the new ICM solves the issue. Thanks again!

It was the ICM, car runs fine now. Thanks!