View Full Version : Rough idle, misfires only when idling

01-22-2017, 11:57 PM
Hello all, I'm slowly sorting out all the little problems with my b5 that I picked up pretty cheap. One thing that's still wrong is the rough idle/misfires. When on VCDS, if I bring the revs up slightly, the misfire count stops. The car drives perfectly fine. I replaced all the plugs and put a whole new ignition coil in with new wires as well. MAF readings are fine. The last thing I can think of is the cam chain tensioners. The misfires will stop on the one bank before the other. Thoughts?

Car is a 98 A4 30v

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01-23-2017, 09:10 AM
Vacuum leak.

Start by checking the pcv piping. It's the plastic hose that connect to both valve covers and goes behind the engine into the intake manifold.

It becomes extremely brittle with age and clogged with oil condensation too.

Edit: into intake manifold.

01-23-2017, 09:51 AM
Yea, I forgot to mention the lines. The previous owner replaced them, but I don't know if he hooked them up properly. I'll put it this way, he JB welded a piece of scrap metal into the oil pan, which I already replaced with a new one. Lol

I'll upload some pictures and if someone can tell me if he did it right or not, that'd be cool.

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01-23-2017, 09:56 AM

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01-23-2017, 10:17 AM
I'm talking about this.


Courtesy of passatworld


Those are the vacuum lines.


Courtesy of Audiforums

And courtesy of searching.

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01-23-2017, 10:46 AM
Alright thanks. I ordered a new pcv pipe as well as a new suction jet pump.

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