[Crvett69]

if the belt had gone enough to bend a valve it wouldn't have kept running before. might have a bad plug or wire on that cylinder. usually a bent valve will make engine run rough since its not firing on one cyl. its possible when they were working on it they took the plugs out or left a wire off or loose, might take it back and have them check their work. or your car might just need a tuneup with new plugs