hows it goin mate, i had this same problem 4 bot 4/5 months and have just receently sorted it

the air intake pipe is ONE problem, there will most likely be carbon emissions or sumin like dat built up in the exhausy manifold, so get dat cleaned. wen u plug it into the computer, it should either come up with lambda sensor, or hall sender. both came up on myn but the lambda sensor dissapeared off the computer once i had changed the pipe, so it was obviously the hall sender, that needed to be changed. wich i got done from audi specialists, cost me bot £300, but id advise anyone to get electrics done by audi, cuz my local garage told me str8 up indirectly he hates knew cars cuz of d electrics, so read between the lines kinda fiing. hope dat helps