Originally Posted by shwndh

I've got a 03' 3.0 A4 and since I've gotten this car about 1.5 years ago, i've had an issue with random misfires at idle. You can't really tell that the car is misfiring at all - the only symptom is that the CEL will come on ocassionally. Here are the codes:

16684 Random/Multiple Cylinder Misfire Detected
16685 Cyl.1 Misfire Detected
16686 Cyl.2 Misfire Detected
16687 Cyl.3 Misfire Detected
16688 Cyl.4 Misfire Detected
16690 Cyl.6 Misfire Detected
19989 Cyl.5 Misfire Detected

And these are the only codes (besides my new intermitent immobilizer issue) I thought I had it fixed last year with several bottles of Techron, but they seem to still be there. Here is what I've done to solve:

1) All 6 coil packs replaced
2) New fuel pump (under recall) & filter
3) New plugs (installed by indy shop, NGK)
4) Air Filter(s)
5) Fixed Vac leak on front of motor (2)
6) Bunch of Techron

I would just watch them on the VAG as the accumulated to almost a hundred before resetting. But after all this, misfires were greatly reduced - they even went away completely after a while (so I though). Then, maybe a couple months later, I just realized that they were still there, it just wasn't enough to throw the CEL. Now they're getting back to the point where they throw the CEL again.

No one on the B6 boards seems to have this problem but me. Was wondering if anyone else with an A6 and the same motor has had similar problems. Worse is that I find out that my CAT(s) are ruined but I'm not trying to throw a bunch of cash into replacing parts just to have the same issue. I'm just going to start with some more bottles of Techron.

BTW I've always used at least 91 octane and full synthetic oil. The engine was very clean after checking the throttle body and valve covers.

Originally Posted by Haxzawbuddy

I have the exact same issue when i got the car it had bad crankcase breather lines and the valve was bad replaced all of them and the vacuum lines still getting the random misfires it starts in cyl 3 then in 6 then spreads to the front of the motor 2002 A6 3.0L

Originally Posted by jcman

Do you have the exact same VCDS/Vagcom codes?

Originally Posted by Haxzawbuddy

Ive only been able to check with obd2 but after many cycles of clearing and idling i only ever get the misfire codes for all cylinders and the random misfire code if the cam sensor was bad would it trip a code?

Originally Posted by jcman

Only if a cam sensor code was present would I be concerned, outside of this the CPS crank position sensor or CTS coolant temp sensor can be a cause without a "hard latch"code at times, MAF and vacuum issues seem to be a more of a common cause.

I hate to say but it's hard to tell without VCDS/Vagcom to see a larger scope of what going on possibly leading up to the misfire problem.

Originally Posted by Haxzawbuddy

Im wondering if the cats are clogged the misfire starts in cyl 3 then goes to 6 and moves forward on the motor until all are misfiring plus the cats get extremely hot within about 10mins of idling i get no o2 sensor code plus the car doesnt want to die it will idle just really crappy

Originally Posted by jcman

Naw, your cats aren't clogged it's the dumping of un-burnt fuel that's going to cook them beyond return, if those cats were slammed the engine power would be very sluggish and the list of relevant codes would be present.

Are the spark plugs newer?

Originally Posted by Haxzawbuddy

They are and they are the reconmended NGK the gap was .010 under the .044 recommended i regapped them and reinstalled them