1988 Mercury Tracer 4 cyl Automatic 64,000 miles

My parents own a Tracer. 2 months ago it was over heating. I took it in to a shop for them and they replaced the radiator. They also replaced a gasket on top of the engine that was leaking oil. I also had them do a tune-up and oil change. I picked it up and it started fine and I drove away. I drove about 30 miles on the freeway, no problem. When I got to the exit and stopped, it sputtered and died. After several tries, it started again and I drove for a while, no problems. Again, at the next stop it died. I took it back to the shop and they adjusted the idle. Same thing continued. It dies or sputters and shakes after it has heated up and I come to a stop. It does not happen if the engine is cool. If I am at a stop and I shift into Neutral it usually settles out but even then the rpms sometimes go down and sputter. The shop that did the work is no longer in there, so I can't ask them to fix it (the car had nothing like this before they did the work).