It seems as though most people get rid of aircon. I've got the aftermarket plenum, so I only have 5 fittings in the back of the plenum and have given away with all of the extras. Anyway, to the point, I just got aircon put in recently - when I flick it on, my revs drop to an almost stall. Was that the IAC valves job? I'm looking at fixing this up so I no longer have rev problems - starting the car with aircon on now is harder obviously, needs a foot on the pedal or else it will stall. Thoughts?

You need an idle control motor or even maybe a simple solinoid idle up that could bump up throttle postion. Does you throttle body have provisions for a idle control motor?(like v6/v8 throttle bodys)or are you still using the original one?

Using XF tb - But I have no idea whether it does or not. I'm thinking it does though because it's got some vac lines that have been blocked up.

AFAIK xf throttle body domt have a iac built in but use a bypass around the butterfly (in the pipe work) to get idle control.Possibly the easiest way would be to put a solinoid on the throttle that bumps up the idle when the a/c switchs on.