air con. woes

I stumbled across this site looking 4 answers (ive heard you lot are the best) anyway? I have a 95 520i , it runs great untill I TURN THE AIRCON. ON then I get poor output from the engine it seems to surge and want to go but something is holding it back i can feel it ,ive changed the idle control valve ,the idler pully (on the air con side ) ,the compressor itself$ ,the auto belt tensioner, with no solutions I think it may be electronic either the DME or the air con control module ,PLEASE any ideas would ease this tied mind of mine.