1990 f250 Starts than shuts itself off.
 

I have a f250 4x4 5.8 automatic. The truck will start run for 30 to 40 seconds then shuts itself off. Through research I thought it was the Idle air control valve So I installed a new one before that cleaned the throttle plates and surrounding areas. The truck started with the same result. The truck will keep starting if I shut it off before it shuts itself off. If it shuts itself off I have to turn the key off and wait. Then it will start and run for less than a minute. Any ideas and help greatly appreciated.