when i start my car its usually ok but i find if i drive and say i go to a movie and come out and start my car again the engine is cold the rpms are at 1500 then rises to 2000, then immediately drops back down and does that same processes over again until the motor is warm and the temp gauge goes to 2 notches and then its over and car runs perfect after that. Can someone tell me what that is and how to fix it? thanks