does it sound like its backfiring? or is there a popping sound in the intake? because thats what my 91 3.1 mpfi did until it stopped running. it stalled one day when it got to operating temp and wouldnt refire then the next day when it was cool it fired right up. until it finally just wouldnt start anymore and it sounded like it was backfiring. check for black soot in your air filter. Edit: i replaced everything that monzaman mentioned and more until i figured out it was a twisted camshaft. so im rebuilding it right now
