I have a 1995 saab 900s 2.3L. When I drive my car the engine does not heat up very fast. if the car is not moving the engine will heat up to the point where it is far past what it would normally be. When I drive my car it stays under where it would normally be unless I turn off the heater all the way then it usually gets to where it needs to be. The check engine light comes on after it has been running for awhile. my heater does not kick out very warm air but the hotter the engine is the hotter the air will be when the car is running. Remember it is winter and cold so I think the air from the outside which is below freezing is cooling the engine when I drive. does this sound like a thermostat problem or heater core or what? btw I am a noob when it comes to cars. Any help in a diagnosis would be appreciated.