Ive got a 01 a6 2.7 and a week ago i was driving on the highway and I punched it and it stuttered then shot out cel code p0304. Got home checked it and then erased it. Came back again doing the same thing. Then while driving around town it would throw the same code but it would feel like I was going over a bunch of small bumps and take forever to switch gears but once it did i accelerated very quickly and it always happened when I gave it a little bit of a punch and it would normally happen right around the 2-3k rpm mark. Now its also stuttering while idling. I have swapped the coil amplifiers and switched coil pack 4 and 5 and its still throwing the same cel code for cyl 4. Need help diagnosing whats wrong.

 

It's a cylinder 4 misfire. Try a new plug. If not that you may have a fuel injector issue.