I have suspected all along that a sensor of some sort is at fault, can you tell me where these are, is it possible to get at them easily or is it a garage job. I will try another garage for a diagnostic. Strangely the car performed ok today but I notice that it does in warmer weather (coincidence maybe!). Noticed also that the idle speed is about what you state but the fault does not appear if it is above 800rpm so maybe a sensor is a bit dodgy below this. Any help with sensor positions will be gratefully recieved.
Thank to all who have contributed so far.