I take back my earlier oil pressure warning light comment.
That can't be it ...
More info: The car was auto, converted to manual ... has all manual bits including ECU.
What sensors can make the check engine light come on ? Everytime the light comes on, it stays on but if the car is switched off and then on again, it resets and the light is off for varying amounts of time, but it always seems to come back.
I have absoloutley no idea why it is doing this! Comments anyone ?