You may want to check your TPS (throttle position switch) voltage at idle. The TPS tells the computer the position of the throttle. It should be close to 0.98 volts at idle. Mine was 0.83V and I had the same problem as you. I turned the idle screw until the voltage climbed to about 0.95V (Close enough for me).
Once you do that, disconnect the negative battery lead for a few mins to clear the cars memory. When you start up the car will start adapting (learning) to the new idle situation. After a couple of minutes or so it should settle down and all should be well. Note that this will not increase your idle RPM (apart from when the computer is relearning).
My car is responding much better now when I turn my A/C on.
Also may want to clean your MAF wire to make sure you are getting proper readings from it. MAF cleaner can be obtained from any parts store.