any of these can contribute to a fluctuating idle. you more than likely have a vacuum leak, are low on coolant, or need to clean the iacv.
-remove the intake and thoroughly cleaned the throttle body with tb cleaner.
-remove the iacv, clean the mesh screen, and "massage" the solenoid. if the solenoid is working perfectly, it should operate when connected directly to the battery. (you will hear it "click")
-reset the ecu.
-check the idle adjustment. is it adjusted appropriately?
-flush the coolant and keep a close eye for any coolant leaks. is the system leaking at all?
-check all the hoses going from/to the throttle body, intake manifold and intake for vacuum leaks, as well as the tb gasket. To verify a vacuum leak, while the car is idling, place the palm of your hand tightly over the throttle body so that it is air tight. the engine should stall out within a couple of seconds. if not, you most likely have a vacuum leak.