DG@Alta

I have recently noticed a bit of roughness at 1950 RPM. It is over a very narrow RPM band and is manifested as a roughness or unbalanced feeling. I don't notice it when driving and it is smooth about 100 RPM on either side. Could this be the dreaded "Evil Buddha Injector Problem"? The car has 13,500 miles and is babied. Am I being paranoid?

DG

S4iowa

And I can guess you're talking about at idle with clutch in or out. Try around 3600-3800 also...and see if you have it there too.

RI A6

And I've noticed that somewhere below 2400 rpm under low throttle settings the ECU wants to run the engine a bit rich, probably to keep the catalytic converter up to temperature for emissions compliance. It could be that it's causing some minor misfires due to plug fouling, which could be the root cause of some of the hesitations the some people notice. (I'm just guessing, though).

You might be less gentle on the engine and run her up and down through the gears on the highway at just below wide open throttle for 10 minutes, and then go back and see if you're still getting roughness at 1950 rpm.

I'll go and do some new logs on my car today and see if there is anything interesting going on.

Do you always experience the roughness?
Do you experience the roughness when the engine is still warming up?
Do you experience the roughness when the engine is up to full operating temperature?

RI A6

Hmm, could it be engine/flywheel balancer?

S4iowa

rather than a misfire rough condition.

And no, the flywheel won't solve it.

There have been a number of people that have felt this with S4's (B6 and B7). Some have had it even after getting a new engine, clutch, or flywheel. I'm guessing more have it than are being reported due to not many people will idle their car at 1800-1900 rpms to feel it. Not to mention the higher range of 3600-3800. And it happens with the clutch in or out.

Those that have worked this vibration issue through the dealer usually get the response that it's "normal".

DG@Alta

I'm in London for the next week but will test all of these theories when I return.

Clutch in or out makes no difference. I don't normally idle at 1950 RPM but was actually warming up the system before I put it to bed for a week. I don't like to run engines for only a few minutes and then shut them down for an extened period. I like the idea of a 'rich' spot in the mixture.

It goes in for a 15K oil change in two weeks so I'll have them check the logs but no engine check lights at all.

Great feedback.

S4iowa

under the B6 and B7 S4 and use key words like vibration and 1800 or 1900.<ul><li><a href="http://search.audiworld.com">http://search.audiworld.com</a</li></ul>

RI A6

I ask. because if you have not changed it since the 5K service, you may be seeing oil breakdown cause some excessive deposits on the plugs. That could cause some roughness.

ELEVENS

I just knew that eventually you were going to blame it on the oil (j/k) -;

RI A6

Actually I think this is the dynamic balance of the engine, especially if it occurs at say 1900 rpm and 3800 rpm (or thereabouts), as that would indicate something harmonic going on.

I'm thinking that it's a low frequency (RPM) resonance in the dual-mass flywheel, that is dampened out at high rpms.