Stock Boy

I was sitting in traffic coming from NYC, and my car started shaking, idling low, and eventually shut off. I had to start it numerous times before it would stay started, but it was still idling low, and it seemed as if the car wasn't getting enough fuel. Took it to Millburn Audi in NJ, and they said they could find no codes, and did a fuel injection flush - $165. They said the car is running 'somewhat' better. I drove off, and about 4 miles into driving - the car started doing the same thing.

I took my car to another shop to get a separate issue checked, and when the mechanic started my car to drive it into the service bay, he immediately said the car is misfiring. He said it could be an issue with the coils, spark plug, wires, or carbon build up. He also found no codes. Has anyone experienced this?

Also - I've done some research on carbon build up in the V8 S5, and it seems to be a well-known issue. I also see some owners were able to get this taken care of through an extended warranty issued by Audi - resulting from a TSB for the intake manifold & fuel injectors. Can anyone verify if this is accurate? Has anyone had excessive carbon build up that was serviced under the extended warranty? I think my concern is not only that my car drives like crap, but that it's not giving me any warning lights, and no codes.