When I am in either PARK or DRIVE, the engine idles low as normal. As soon as I put on the air conditioning, the engine immediately idles higher (2500 rpm) then down (normal), up and down, up and down. This continues until I turn off the air conditioning. This makes it necessary to apply the brake harder when waiting at lights, etc. as well as being an abnormality I want to fix. Turning on the fan instead of a/c does not cause the excessive idling. Can anyone identify or assist? Thanks.