I bet your AC dosent work too good does it?? If this is the case,, it means you have a low AC freon charge..The AC system has a low side pressure switch that engages the compressor at approx 50 lbs.When you hit the AC switch it sends a signal to the PCM ( powertrain Control module) to increase RPM ( sent to the Idle Air Control valve) to compensate for the added load on the engine due to compessor and fan draw..What I think you are experienceing Is a restriction in your high side Ac SYSTEM, so when you hit the AC button on,, pressures look good, PCM adds RPM,, A/C low pressue switch sees low pressure,, due to blockage, shuts off compressor, PCM still sees AC On,, Idle speed increases, due to lack of Engine Drag,, idle goes up,, till pressures in the low side and turn Compressor on,, Idle speed goes down,, are you confused now>?? I sure am You guys think this mechanic stuff is easy?? Crystal Ball still broke here.. See your Dealer, pay the money,, dont be cheap,, will cost you more in the long run..