# Missfire at Idle



## VWLover1985 (Nov 19, 2008)

Hello,

Ive got a 1999 audi a4 2.8 quattro that has been giving me nothing but a head ache. The car has a missfire at a idle only. No missfire through the midrange at all. Ive replaced the ignition coils. The injectors were replaced. Ive heard some things about a ICM and that there are 2 of them. If so where are these located. Ive checked the compression, and everything is ok on that end. The missfire is also only on bank 1 (1,2,3). Ive been doing alot of research on this but im looking for some inputs on what you guys might think it may be. Im not very familiar with the 2.8 V6 motor.

Thank you


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## O_o (Nov 12, 2009)

Most often, misfires at idle only are due to unmetered air. A vacuum leak would misfire on all cylinders, so I suspect you may have a leak at the base of the intake runners on the right (passenger) side. There are other possibilities though -- what else does your scan say? Any messages from O2 sensor(s) or the MAF sensor?

FFR: for this engine, a bad coil would misfire on cylinder pairs on opposite banks (1&6, 2&5, or 3&4).


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## VWLover1985 (Nov 19, 2008)

Hello,

I got a random cylinder missfire code, and cylinders 1-3. Those are the only codes I got. As for me replacing the igntion coils, I replaced those last month because they were bad. I just got in from the garage from looking at it, and ive noticed on that bank when the car is cold that the head is quite noisey just on the passengers side. The right side is quiet. I hate to explain it in such simple terms but there is not other way to explain it. I've looked for some simple vacuum leaks but came across short handed. Im gonna check out the intake manifold right after this message and I will let you know.

Thanks for the help so far.


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## O_o (Nov 12, 2009)

Hmmm. Usually an intake/vacuum/PCV leak throws a code for one or more O2 sensors, and/or the MAF sensor, especially if it's bad enough to cause misfires. You'd also probably hear a sucking or whistling noise. Can you describe the noise a little more? Tapping? Popping? ... ?

The only other things I can think of offhand that would cause misfires on just one bank are if the cam chain or timing belt slipped, or, if your PCV system is constipated enough, the valve cover gasket will leak, and the plug wells fill with oil and foul the plugs.


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## VWLover1985 (Nov 19, 2008)

Hello,


Yeah I have plans on checking the belt and such today. Now that you say it the valvecover gasket does seem to have a bit of a leak. On that bank ive seen some oil on the ends of the plug wires. But it doesnt seem enough to cause a missfire. The noise sounds like a VR6 with raspy chains when its cold. When it warms up and if you hold it at a steady rpm say "3000rpm" it has a slight tap.

At this point im not sure what to think.

Thanks again


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## VWLover1985 (Nov 19, 2008)

Ok,

So I pulled the valve cover and found rubbing against the back side of the chain a orange/brown piece of plastic about 3/4 in long. So at this point I knew something with the tensioner or of that sort is broken. SO I looked on the cam follower and seen the arrow on each (assuming those are to time the cams) I turned the crank to line these up and to what im seeing the cam closest to the center from the markings appears to be off a tooth. Clearly it looks like ive found my problem. Now onto finding what the broken plastic is. It doesnt look like its from the slide that the chain rides on. Any ideas? You've been alot of help.

Thanks so far


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## O_o (Nov 12, 2009)

Maybe the piece you found broke off the other chain guide, the one underneath? I think mine was black, but I could be wrong, or they may have made them in different colours. If it looks like it's the same colour as the upper one, I think that's the most likely culprit. In which case, it looks like you need a new cam chain tensioner, which sucks, because they're surprisingly expensive on the 30V.

I haven't seen the inside of one of these engines in a while, but IIRC, to check the timing, at TDC, the arrow on the exhaust-side cap nearest the chain should line up with the notch on the sprocket. If it does, then your belt is OK. From there, you should count 16 (I think - not 100% sure) links (inclusive) to the notch on the intake side sprocket, which doesn't always line up exactly with the arrow, but should be close. If it's off by more than a full link, then your chain must have hopped. I'm not sure if you can tell if the tensioner is fubar just by looking at the alignment.


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## O_o (Nov 12, 2009)

BTW, since you'll be putting on a new valve-cover gasket, you should swap out all the PCV hoses, and check the PCV valve. These cars have a bit of a reputation for PCV clogs causing the valve cover gaskets to leak.


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