I have a 2002 B5 S4, it is running really ruff. I had driven it all day and there was no problems. I had gone to an appt, started the car and it started misfiring. It is misfiring in cycl's 1,3,4 and 6 the code that it comes up with is P0300. Anyone know where I should start to look to fix this problem.

 

Look at the throttle body boot, or for another major vacuum leak

 

I had the same codes with my 02 Allroad. seemed to get worse by the day. It started with the odd miss under acceleration and after a few days it started to miss while idling at stop light. It turned out to be old spark plugs with cracked ceramics. Try new plugs. $26 each for platinum $$ good luck !!