Hi Marc
Aircon increases the engine load, so to avoid the idle speed dropping too low the ecu increases the throttle opening to compensate, although it overcompensates by design so you have an increased idle with the ac turned on.
I'd start by looking at the throttle body, that probably needs a clean, especially the butterfly, and also give the MAF sensor a clean. (not sure what has happened to the photos, I'll see if I can fix that.