I have an '05 C6 LS2 A4 with approx. 75,000 mi. 2 days ago i was passing someone and put my foot deep in the gas pedal. The car responded great as usual but right before I was going to let off of the accelerator (total time on floor approx. 4 seconds) I heard and felt a loud PPHHFFF! sound (like a carb would sound backfiring in the engine bay) and the car immediately started running horribly, like it's running on 5 cylinders. It's still running the same. Obvious finds, that may be unrelated, exhaust pipe had become seperated at one joint on one side where two peices join together. Spark plugs look ok...there is gas in the intake plenum. That's all the info I have...any ideas? thanks.