I thought I had it

How old is the car? The chances are your cat could be on its way out, consult a garage and ask them to stick their sniffer up the pipe, they should be able to tell you if it's in good health or not.

I woudnt rule out the lamda probe being worm out either - they only last so long

sorry forgot to say 1993 car, lambda sensor replaced 5 months ago with genuine replacement not cheap rubbish one. only code 123 shows everything else ok

The condition of the cat has got nothing to do with the Lambda system. There is no sensor downstream of the cat, so the system cannot tell whether the cat is working or not. In my experience cats never wear out - not in 390,000 miles anyway. I would suspect a poor electrical connection somewhere. Is the engine properly earthed - there is supposed to be a separate small braided earth lead to the top of the engine. For some reason the main starter earth is not sufficient.

I replaced the earth lead that goes from the rocker cover to the firewall with a volvo one all the way from sweden. that was how i was able to do the 20 miles without the light coming on. i am thinking it must be a loose connection to the ECU

Hi Did you read the Codes in the ECU as per "700/900 FAQ" ivor940