start-up fault on rover 416 'R' plate ?

Engine fires then cuts out. Have had the fuel cutoff bypassed, worked for 3 days then wont start again. Once running it is a good engine. But with a value of only £400, I need a cheap, quick fix. Have tried combinations of fob & key to open it, sometimes this clears the fault & sometimes not. I am getting fed up with it, need it as I am carer to my disabled mother.
Rover 416 SLI, 1.6 'R' plate.