Past few days my car has had a very poor start up, keeping its idle at a rough 500. If i put into gear, and give some gas, when the rpms drop it cuts off. I have gotten a standard tune up, fuel rail cleaning, and when I took it to a shop.. their response after a 80 buck diagonostic is they could not duplicate the problem. It happened again after work today, and I have no idea what it could be. Help the car noob please!!!