Sigma High Hot Idle

[Dorset7]

I seem to be having an issue with high tick over on my 125 Sigma when it's hot. I've adjusted the idle speed on the idle screw on the the standard single TB to the point where the car is struggling to tick over cold but runs about right (900-1000rpm) when hot.

It would seem that as the car gets hot the tick over rises and pulses (hunts) around the 1200-1300rpm mark. I've reset the ECU using the FIA key method and I've checked all the linkages are free and lubricated. There doesn't appear to be any restriction on the return of the cable and I'm at a bit of a loss.

I've checked that everything is tight and there doesn't appear to be an air leak anywhere.

The car is behaving very well under power and this is more of an irritation than a major drama but I would like to try and pin it down and get it nipped.

I'm stumped, any ideas?

[Tom_Arundel]

Its not quite as simple as backing off the idle screw, the throttle pot needs to be set correctly for throttle position and its very sensitive at closed throttle. But first check MAP sensor pipe and crankcase breather pipe for cracks/security, the MAP pipe will be cracking/splitting if it is more than a few years old. Otherwise could be many things!