Engine chugs and loses power after thermostat opens. on 1990 Isuzu Pickup

engine runs great untill thermostat opens up. then begins to "chug" and loose power to the point it dies. BUT! if you shut the key off (while rolling in neutral) and wait a couple seconds and start the motor again it runs great for a minute or so and does it again. i believe its a vaccume problem of some sort. not sure where to start looking.

Asked by for the 1990 Isuzu Pickup
could be a bad distributor
That is possible yet why would it temporarly "heal" its self by shutting off motor and restarting it? Would the vaccume advance change timeing while running and by shutting off engine allow it to reset upon start up?
the module inside the distributor gets hot and shuts the engine down when it shuts down check for spark