First, go to a do-it-yourself car wash, and power wash your engine bay, especially the space between the radiator and A/C condenser. This will improve air flow and also give you a clean work space. Then, buy a can of Gum-out, and spray all around your intake manifold and throttle body with the engine running. If there is any kind of external leak, the spray will cause you idle speed to change and voila, you have figured out where to concentrate your labor. Also, with the spray, clean out the throttle body, idle air control valve, and PCV hose. Idle speed is controlled by temperature and by the computer. Also, make sure that the battery cables are perfectly clean on BOTH ends. Voltage inconsistencies will invariably cause troubles like this. Good Luck!!!