Well I thionk that your problem its the IAC (idle air control valve/motor)
there are two idle speed adjustments to control idle on our cars. First is the manually adjusted base idle setting, which determines the minimum airflow through the IACV (and minimum warm-idle speed). Second is the ECU's control over the "trim" valve within the IACV, which compensates for hot and cold idle and engine loading (power steering and A/C operation).
I think that the Valve stick open once you turn on the A/C and stays that way.
Check that, clean it and replace it if faulty, be sure to adjust it ( it should be fully seated (the package should tell you the way it will be adjusted)
any other question do not hesitate to ask good luck and let us know if that solve your problem!
Thursday, January 3rd, 2008 AT 2:23 PM