Hi all,

Looking for some advice. Sorry about the lengthy post but wanted to give all the info i have.
We bought the A6 at an auction about 3 months ago so have no service history.
So, to get started here is the car info:
2002 A6 Quattro Sedan 3.0 V6 Auto
158,000 miles (250,000km)

Background:
A couple of months ago CEL came on with Cyl 2 misfire and there was a slight misfire noticeable.. Replaced the coil pack and all was well.
CEL came on a couple of weeks ago - code P0431 warm up catalyst bank 2 efficiency below threshhold. I should point out the car was running great. I cleared that code.
In the meantime I changed all the plugs with iridium tipped ones. Also changed air filter.
The CEL came on again a week later - P0431. Again, I cleared the code. I figured now I got to fix this and have started to do some research even though it is still running great.
So yesterday my son had the car (I was not there). He started it - apparently a bit difficult to start. As he pulled out of the parking lot it started mis-firing very badly, no power and the CEL flashing. He stopped and shut the car off. He restarted it and it ran fine. Would never know it acted up except the CEL is back on (not flashing). I drove the car to work today (40 miles round trip) and it ran fine except for the last mile where the engine was no longer idling smooth. In the garage, in park, at a very light throttle the RPMs osilate between 800 and 1000. At heavier throttle it seems smooth (this is a new symptom).

These are the codes it threw:
16684 P0300 Randome multiple cylinder mis-fire
16689 P0305 cylinder 5 mis-fire
16688 P0304 cylinder 4 mis-fire
16687 P0303 cylinder 3 mis-fire
16685 P0301 cylinder 1 mis-fire

So, only cylinder 2 did not throw a code - the one with a new coil pack.
After that long winded description - looking for suggestions. Can 5 coil packs go? Is it somehow related to the P0431 code? Hoping I can get some suggestions with all the experience on this forum.

Thank you.

 

Swap the coil pack from cyl 2 to one of the others that has a confirmed misfire.
Clear codes, start vehicle, await the dreaded engine light, re scan and see if there's a change, if same codes are shown its most likely not the coil packs. If the misfire is now on cyl 2 and not the one you swapped out, it's the coils.
When you changed the plugs did you gap them?

 

Yes, did gap each plug. I just ordered a complete set of coil packs. I will keep the #2 cylinder pack as a spare. I decided that if the #2 could fail then they were all likely past thier prime. I am also thinking the misfire could be causing my P0431 code if there is raw fuel going out the exhaust during the misfires. I will keep you posted if this fixes the issues. With the new e-test rules in Ontario this year will have to get this sorted or it will be a fail regardless of what comes out the tail pipes.

 

Sorry don't know which engines are direct injection but if yours is, I would get a carbon clean done - carbon build up on valves and stems causes air flow issues which can cause misfires, CEL's, etc.

GL and let us know the ultimate cause...

 

coil packs on these cars are finicky and if one acts up they all tend to do it. I am hoping this is the same thing in your case. Replace them all and see what happens, you said you gaped the spark plugs properly so thats all I can think of really.

 

I appreciate all the feedback.
I have replaced all the coil packs and I have had no issues in the last month. Oh and yes, I did gap each plug. I was getting a CEL every week for what seemed to be the O2 sensor (forget the actual code) . Since the new coil packs - nothing. I am thinking they have been misfiring and possibly dumping unburnt fuel down the exhaust upsetting the O2 sensor - maybe? For the most part the misfire was very subtle - except in the incidence in the original post. Anyway - all good for now.

Cheers,

 

I am hoping this is the same thing in your case. Replace them all and see what happens, you said you gaped the spark plugs properly so thats all I can think of really.