1986 Buick Skylark My 1986 Buick Skylark dies at stops and

I know I already asked this but to update, the mechanic says he tested everything, like ratmatz mentioned, he said, it passes smog and the diognostic test says there is nothing wrong anymore after replacing the fuel injectors and the exhaust manifold. He says that he checked a list of things I can't remember all he said, but, he said, maybe it is the timing? Could the timing be making my car die at red lights and when it does I put the car into Drive and then it dies. Only after it has ran a while.
He test drove it one day total then he test drove it a couple hours today, I picked it up and it ran fine for a couple of hours then it died when I filled up. He is stumped he said, he had to wait till the second to get a special tool to check something with the balance with the piston? Or the timing or something so he can see if it is that. For three years people have tried to fix this car and noone knows what is wrong if anyone can help I would appreciate it I have interviews I am missing because my new car keeps spending all its time in the shop. Or if you know anyone who wants to buy it so I can just buy a new that is exceptable too. But, I don't want to sell someone something that is broke. So either or I appreciate the help. Thanks Terri