1994 Volvo 850S Stalls at Any Speed

This is a 5-cylinder engine with 70,000 miles on it. It stalls out at any speed, usually when I let up on the accelerator, but not necessarily only then. At times I only need to wait 3 minutes to start it up again, but this morning I had to wait 30 minutes. The engine would not even turn over. This seems to be related to how hot it is outside–the higher the temperature, the more likely it is to stall out, and the longer I need to wait to start it up. Sometimes I can go for a whole week without any problems, or sometimes it can stall out 3 or 4 times on one trip to the store.

I have brought to several garages and they cannot recreate the stalls, so cannot put their sensors on anything, so cannot diagnose the problem. This is a car without an ignition module–only a coil, and an alternator. There was one occasion when I avoided a stall out by pumping the gas really furiously, but this has not worked any other time. so far. When the engine goes, all the power goes out too–the steering, the shifting, etc. Sometimes it seems if I wait a while and let the car “warm up” in the drive way before heading out on the road it stalls less–but that may be in my head.