1993 Vauxhall Corsa Intermittent Stalling

Engine Performance problem
1993 Vauxhall Corsa 4 cyl Front Wheel Drive Manual

It's Corsa and runs like a dream except when it doesn't. It'll suddenly just cut out (sometimes even resetting the dash clock). Doesn't seem to be any pattern to it's stalling. Have 'paper clipped' the error codes but nothing there.

Have replaced:

Petrol pump (garage said that that was it)
Engine coolant sensor (online forum suggested)
EMU
Airbox (vacuum controlled pre-warmer flap was not working)

and after each of these repairs the car ran fine for a day or so and then started playing up again!

Garage claims to have checked everything and they have no idea why.

Suggestions please

ps. When we got the car the contacts in the dizzy cap were a bit black and I cleaned them up.