I had an intermittent ignition problem on a Reliant. The garage wanted to do $400 worth of guess work including checking the air in the tires to stop the stalling. I said no thanks, went and installed a new Hall sensor. End of problem. My point is, if the problem is intermittent, what are your chances of testing the sensor at just the right temperature and other conditions to see the problem? If the ignition was totally dead such a test would help. The test process is given in the Bentley manual, section 280-9. If you have that manual you can try it. By the way, the manual says DON'T DISCONNECT THE CONNECTOR AT THE CONTROL UNIT. Apparently this destroys the "one way guide sleeves" requiring the replacement of the wiring harness. I haven't tried it so I can't speak from experience. you might just try a new Hall sensor.