Engine light problem on 2004 Mitsubishi Colt 1.1

We have a 1.1 2004 Mitsubishi Colt that has an engine light fault.

The check engine light usually comes on after the car has been parked (after use) for 30 mins and when restarted the light comes on and there is little or no throttle response and car won't move, ''Limp home mode?''. If we turn car off and wait 5-10 mins the car will restart and run OK but engine light stays on. If car is left for a long while the light will not come on when restarted but the fault will return after 4-5 days.

Can anyone please shed some light on what the problem is as the local main dealer says they can't do nothing unless we turn up with the light on. As is usual with these things the problem happens at weekends or evenings.