I have an 03' Mustang GT and I have had a misfire on Cylinder 4 according to the computer code from the dealer. It happens when I get on it, and at a high RPM it will all of a sudden chug, and when I let off the gas it seems to return to normal. The problem has occurred three times and the service engine soon light comes on. The dealer can not seem to fix the problem. Has anyone else had this problem?? Also, is this misfire doing damage to the engine?