Yeah, I had the same problem and the ignition coil was the cause. You should first check for good spark. If the spark is weak then you know that you need to replace either the coil, wires, distributer cap and rotor or something. But since it is heat related, the coil would be the most probable culprit.

When I had my problem, I looked at the spark, even when though it was cool out and the car wasn't exhibiting the problem. Comparing it to another 240, it seemed very weak. After swapping out the coil, the spark was huge! Like it should be. So, I replaced it and the problem went away.

If you check for spark and everything seems OK, then you might want to suspect the fuel pump relay. In hot situations the typical bad solder joints could cause a drop in voltage to the pumps and cause a similar problem.