I've had a small problem with idle since the PowerFC was fitted - I am just posting this here to get some ideas, until I can see Ryan again because it might not even be to do with the PFC itself, may be a coincidence but it did happen right afterwards.
What happens is that the engine will randomly rev to over 2,000 rpm when I am at idle, if and only if the air con or lights are on, i.e. there's extra load on the engine. However, if I am already at a good idle (800 rpm) and I switch the lights on, the revs increase to about 830 as normal. It's only when I blip the throttle that the revs go high.
Sometimes the revs will drop back down again after a few seconds, then back up of it's own accord.
Ryan's suggested a sticky idle control valve. Would the explain the revs sticking high AND randomly going low and high again?