Hello all. I have a problem which my Audi specialist doesn't seem able to fix. My A4 Avant 1999 Auto has done 180k.

At 2000 revs on the motorway (approx 60 mph - seems to have to be at a constant speed) it judders every 15-20 secs - the rev counter jumps as if I had briefly touched the throttle - this happens in time with the judder. It also does it at both lower and higher speeds but the judder is not so noticeable. Above 80 mph the problem seems to disappear.

Any ideas? Simon