Has anyone looked at (replaced or resoldered) the fuel pump relay and the radio suppression relay? They are both very common problem areas and neither one will leave a clue in terms of fault codes.

Hint: If the engine dies and won't immediately restart, listen for the momentary fuel pump noise when you first turn on the ignition. If you can hear the pump(s), then that relay is likely OK and you should look to the radio suppression relay. If your car has two relays mounted on the front side of the radiator overflow bottle, then one is the radio suppression, and the other is for the aux electric fan. They are identical relays, so you can swap the wire connections between the two to see if it brings the engine to life.