Audi a4 2.6 backfires when accelerate?

Have the OBDII ran, take it to a advanced auto parts to see if there is a code you may be running rich, or a number of other problems my Audi had a minor misfire which didn't flag the check engine light but caused an occasional backfire because the fuel was being exhausted. If the engine shudders it could be a misfire. Or its possible that your intake filter is clogged.