An update. I removed the stepper motor (idle air by-pass valve) and cleaned it again, but also its housing, and cleaned everything with carb cleaner. Re-assembled and bingo, idle behaves perfectly. I must say neither was very coked up so I'm thinking it might have been a particle trapped between the valve and its seat ??
Thanks for the replies, regards, John.
Thanks for the fix result John, you never know when mine might start playing up some time.
