7A Engine Vibration between 5-6k Revs

[cexley]

My 7A 20V Quattro Coupe has a lot of engine vibration between 5000-6000 revs. Up to 5k is smooth and from 6-7k redline is also smooth. The engine pulls normally through the rough patch. Any ideas? I've checked engine and gearbox mounts and replaced nearside gearbox mount which looked tired. I'm now beginning to think it is a faulty sensor feeding duff info to the ECU. Of course, this may be 'normal' for the 7A, in which case, someone put me out of my misery.

[Error404]

I'd first try cleaning the Airflow meter elements with some carb cleaner and checking the ignition leads

[Rusty]

Could be a bush in the driveline too or the clutch or indeed a change in anything that rotates. Hope it's something sensible, give it a good once over and it'll be right!

[mcandmar]

It could be the exhaust hitting the body, 5-6k rpms is the range the engine moves about the most. Check the downpipe joint bolts as they are very close to the heatshield on the subframe. Under load that joint moves up in the car getting even closer, and in my case resting against the heat shield. I had to rotate the flange on mine and shorten one of the bolts to stop it.

[simon44]

Hi, I get a vibration at these revs which I've put down to it being a 5 cylinder but maybe I'm wrong. Previously I did experience the vibration from the heat shield which we have rectified so it is smooth again at all other revs.

[stiglet]

I would say engine mount for sure. When were they replaced?

[anton]

stiglet has motorsport engine mounts and the vibration at this point is very harsh, i think it is a normal 7a think, maybe to do with the reasonance of the longer runners on the intake?
either way i would be looking in the direction of worn mounts....

Ant

[cexley]

Now changed all gearbox & engine mounts. All the old mounts looked OK. Things now feel a bit tighter, but vibration is still there. Now analysed the symptoms more closely and noticed that the car drives fine until it gets revved into the 5k + range. It then loses a lot of low and mid range pull and the power delivery becomes 'flat' and has to be revved through the midrange to find the power. It is when this happens that I notice the vibration coming in at higher revs, so I think the vibes are a side affect of a possible fueling and/or ECU problem that manifests itself when being driven hard or engine gets hotter.

Both knock sensors and the temp sender replaced (which cured random power backing off issues - see earlier thread) so could it be lamba? It would help if my VAG-COM would actually pull the codes from a 7a, but unless I am doing something super dumb, the Hitachi ECU won't talk (unless some genius out there has found a way to persuade a 7A to confess its hangups to VAG-COM).

[Error404]

The early 7A doesn't work with vagcom, but you can read the fault codes with a blinker light

Try this: http://www.20v.org/fault.htm

[newsh]

Could it be a worn harmonic damper? Does the bottom pulley wobble when you rev it?