I used to have that problem in my 84 before it croaked, when the car was really hot it wouldn't restart and would idle rough, i was told by a mechanic that it is most likely the injectors overheating, my car was running very hot, but i don't know i've never had that problem since, i would try running fuel injector cleaner through your fuel system and see what that does, you may also want to change the fuel filter they can get pretty dirty if its never been changed before.