Try the idle relearn. If your car is new or if your battery get disconnected and at a few other occasions you car can "forget" it's idle tables. I'm not exactly sure of the exact process but it should be in the manual. I know its involves starting with a cold motor and letting it idle till warm for about 5-10min and then turning on the ac for 2 min.
---------- Post added at 09:04 PM ---------- Previous post was at 09:02 PM ----------
Because your vehicle's engine is electronically controlled by a computer, some control conditions are maintained by power from the battery. When the battery is disconnected or a new battery is installed, the engine must relearn its idle and fuel trim strategy for optimum driveability and performance. To begin this process:
1.) With the vehicle at a complete stop, set the parking brake.
2.) Put the gearshift in P (Park) (automatic transmission) or the neutral position (manual transmission), turn of all accessories and start the engine.
3.) Run the engine until it reaches normal operating temperature.
4.) Allow the engine to idle for atleast one minute. *AM note: one minute AFTER you get to peak temperature - probably about 5 minutes total from cold start.
5.) Turn the A/C on and allow the engine to idle for at least one minute.
6.) Drive the vehicle to complete the relearning process.
• The vehicle may need to be driven 10 miles (16km) or more to relearn the idle and fuel trim strategy.
• If you do not allow the engine to relearn its idle trim, the idle quality of your vehicle may be adversely affected until the idle trim is eventually relearned.
I just did a copy/paste for a google search. Not my personal info or words.