When the car stalls, have a ohm-meter handy and immediately connect it across the plug for the crank position sensor (at the ignition control unit). As the engine compartment cools down you can watch the resistance change (on a defective unit). I caught a bad cps that way, one that had stranded the owner, a few minutes at a time, whenever and wherever, over many months. What surprised me was that the hot resistance was nearly zero and as it cooled the resistance climbed higher until some threshhold value where the car started. I witnessed the same resistance change several times the same day (the day that the car was delivered to the shop and literally would no longer stay running for more than 5 minutes or so.)