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Old 04-30-2014, 04:34 AM   #1
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Default 2004 A4 Cabrio 3.0 V6 Random Multiple Misfires

Had the car 18 months now and been trying to eliminate a flashing CEL for most of that time.

Codes indicate random multiple misfires on just one bank, 4,5 & 6.

So far:
New coil packs (Audi) Under recall on 10 year old car - thumbs up!
New MAF sensor (Audi)
New vaccumm pcv valve
New brake switch (Audi)
New Plugs (Bosch)

General inspection for vacuum leeks but this only happens when driving and the 'misfires' aren't noticeable so very difficult to trace.

Random/multiple cylinder misfire detected P0300
------------------
Sporadic 001-upper

Cylinder 4 misfire detected: P0304
------------------
Sporadic 008 - implausible

Cylinder 5 misfire detected: P0305
-----------------
Sporadic 001-upper limit exceeded

Cylinder 6 misfire detected: P0306
-----------------
Sporadic 001-upper limit exceeded

Any ideas/suggestions much appreciated.

Mark
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Old 04-30-2014, 08:55 AM   #2
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Default

I did of course mean 'leaks', although I do live in Wales so you never know. :-)
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Old 06-14-2014, 09:25 AM   #3
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Default Getting worse!

Well, since originally posting the car will now occasionally start running really rough - hunting at idle wildly, from stall to 2,000 revs like it's desparately trying to control itself. Sort of runs OK once you get going. Has usually rectified itself within a few minutes but recently it stayed like this. All sorts of codes, not just the misfires, O2 sensors, MAF sensor etc accompanied by CEL and, strangely. ESP lights.

Managed to limp to the main dealer as starting to get fed up with it. Guess what - they started it up and it was fine! Loads of codes though. They kept it for two days, said they spent hours on it, changed a 25 power relay (??) charged me 750 (ouch!) and it has been fine for a couple of weeks, then multiple misfires, blinking CEL and yesterday cough, splutter, really rough idle again.

Spent most of today pulling everything off the top, including rocker covers. Cleaned all connectors, crank breathers, checked vacuum lines, plugs etc etc.

Now drives and idles OK but still getting random misfires on one bank (strangely only 4 & 6 now)
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Old 08-12-2014, 07:53 AM   #4
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Default Ive had the same problem on a Mercedes C Class

Hi,
I had exactly the same problem with a C Class Mercedes, I did everything that you have with no joy. Eventually it came down to a crankshaft sensor. They can crack with age / heat and cause all sorts of problems including the engine hunting, loss of power, running rough etc. I'd try that.

Good Luck
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Old 08-12-2014, 09:25 AM   #5
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Default

Thanks for the tip. I did get to the bottom of it. After doing all of the above plus inlet manifold and throttle body gaskets, cleaning & swapping injectors it had to be timing, catalytic converter or some odd issue with the ECU... took the timing covers off and saw the tell tale signs of a bodge job... tipex marks rather than audi cam locking tools.

Retimed the car and now runs better than it ever did.

What threw me was the intermittant nature of the misfire. Turns out it wasn' t that intermittant, pretty much all the time but only occasionally tripping the CEL, plus the variable valve timing can do great job of hiding the fact the timing is slightly off most of the time... only in certain conditions was it really noticeable something wasn't right. My experience of older cars without variable valve timing is that if the timing is off, it's off and the car runs like a bag of spanners.

Anyway, very happy now :-)
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Old 08-12-2014, 09:25 AM
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