Why does my car run smoothly when it is cold and miss at a stop light when it is warm and has been running for about 10 minutes? It doesn't happen at the same interval of time, but will occur when it is warm. It seems after about 20 minutes at 45 mph to jerk. I assume that it is missing. The engine has not stopped and died out on me. This problem has been going on for about one and half weeks. When I took it in, the auto shop said is was running fine and it wasn't missing. However, away from the shop - it starts having the problem of missing. Need help, any answer?