Your vehicle is equipped with an idle control system that is controlled through the ecm. If there is a fault in the system it should throw a trouble code. It is possible that you have an issue with the Idle Speed Control solenoid. You can test the solenoid using a digital multimeter that can measure resistance. Disconnect the the harness connector from the solenoid. Set the multimeter to the 200-Ohm scale. Now measure the resistance between the connector terminals. (I have a picture below to help you out.) There is a diode in the solenoid. Connect the multimeter positive test lead to the VPWR terminal and the multimeter negative lead to the ISC terminal. The resistance should be 7-13 ohms. If the resistance doesn't fall in this range then replace the Idle Speed Control Solenoid. I priced this item on Auto Zones website and it lists for around $50. Let me know if you have any other questions. Thanks.