abcxyzzz

Hi, i have a 2004 Audi A4 3.0L Quattro Avant. I noticed something weird recently when i drive the car steadily around 2000 rpms, the rpm/engine will frequently go up and down between 1800 and 2000. RRRrrrRRRrrrRRRrrrRRRrrr, until i get out of the 2000 rpm range.

Anyone know what's causing that and how to fix it, or if it's any cause for great concern?

Thanks.

the_duke

First thing I would do is a VCDS scan.

vulkus

There is a similar issue with the 1.8 Turbo's. Does this only occur when the engine has warmed up? Does it do it when cold?
If it doesn't do it when cold, try swapping out the crank position sensor, as they age they they break down with constant hot/cold cycles, and will cause all sorts of problems and not throw their own code.

the_duke

You could just replace things and spend a bunch of money. Or you could start with a proper diagnosis.

abcxyzzz

Seems to happen regardless of whether it is hot or cold. I recently had the crank position sensor replaced because the car was ocassionally not turning over when trying to start it and replacing the crank position sensor fixed that issue which was about a year ago...

John535is

It shouldn't fluctuate (neither the 3.0 or the 1.8T).
You need to get a scan (refer The _Duke advice). If you cannot get hold of a VCDS or VCDS lite, any scanner that does VAG cars is a start.
My first thought is a vacuum leak. Start checking all the tubes and connections. They often crack near the joins.

2003Quattro1.8T

Had this exact same problem...i isolated it to a worn out Air valve that was holding on by a thread...once i got it replaced, all was good. I never threw a MIL either...