Mitsubishi Repair: Stalling, coolant temperature sensor, mass air sensor

Question
1995 eclipse RS 2.0 non turbo . Installed new Head gasket, water pump , timing belt . I am having a problem after about 15 to 20 min of operation the car stalls if you try to restart it run rough and backfires them will stall if the car sits for 5 to 10 min. it will restart and run for a few min. then stall again it appears to be related to engine temp . Starting from cold it runs smooth all issues start after warm up Need to know where to start trouble shooting at

Answer
Todd,
I would guess you have a malfunctioning Idle Speed Controller (ISC) or a bad engine coolant temperature sensor.  If you have a service manual for your car (and you can pick one up at most major auto parts stores), it will provide instruction on how to test those items.  Other items to inspect are your trottle body, throttle position sensor, Mass Air Sensor, and even the car's computer (ECM).  All of these items vary the idle speed and performance of the engine when your reahed normal operating temperature.  
Good luck!