Hope someone can help. my a6 2.8 quattro has a misfire/hestitates at between 25 and 20 thou rpm. runs great at above and below and as usual with these issues the car sometimes is ok but other times not. Problem has progressively got worse over last 18 months - now covered 128k. Audi could,t diagnose neither could diagnostic check. Any ideas??
PS - also had issue with horn intermitently going off on own and simultaneou sound of clicking (like a short/relay) in area at hub/base of steering wheel....easy solved by removing horn fuse (-: however anyone else had this issue??

 

it could be an air leak/dirty clogged fuel filter/ engine compression/ fuel pressure delivery rate if you have done mods/coil arcing

 

Have you checked your breather line that runs around the top of the engine?

http://www.audiworld.com/tech/eng79.shtml