I appreciate this isnt the A6 forum but as the car in question has an engine very similar to the S4 thought I'd have a go at posting here first as it probably gets more traffic than the A6 section! Car in question is a 2001 A6 Allroad Tiptronic 2.7T with the 250 bhp 2671cc biturbo V6 engine (very similar to the S4 engine hence the posting here) purchased last week by my stepfather and is slowly being looked over and serviced etc by me. It starts and runs fine, except for an occasional judder. It isn't a regular occurrence and can occur both under load and on the over-run. It doesn't sound or feel like a mis-fire, the whole car just shakes for a fraction of a second when it occurs. As the car is a Tiptronic, I thought initially it could be a gearbox problem , but it happened today with the car stationary at the traffic lights so am inclined to think it might be an engine problem? Before we start taking it to a garage to see if there are any fault codes recorded are there any easy checks I could do at home? The car did in its recent history did have repair work/replacement Lambda probes if that is of any relevance. Am hoping that he hasn't bought a pup, so any advice appreciated..... Thanks!