Hi there!It is likley the IAC valve.Sometimes it gets covered with carbon and the pintal inside cannot move to make the adjustments.You can usually take it off and clean everything up with carb cleaner and that will allow the pintal to move properly.Here is some info.Hope it helps!Thanks
See Figure 1
Fig. 1: IAC valve assembly
The Idle Air Control (IAC) valve adjusts the engine idle speed. The valve is located on the side of the throttle body. The valve is controlled by a duty cycle signal from the PCM and allows air to bypass the throttle plate in order to maintain the proper idle speed.
Do not attempt to clean the IAC valve. Carburetor tune-up cleaners or any type of solvent cleaners will damage the internal components of the valve.
See Figure 2
Fig. 2: The IAC can be monitored with an appropriate and Data-stream capable scan tool
Due to the diode in the solenoid, place the ohmmeter positive lead on the VPWR terminal and the negative lead on the ISC terminal.
REMOVAL & INSTALLATION
See Figures 3 through 9
Fig. 3: IAC valve mounting-3.0L OHC (4 valve) engine Fig. 4: Detach the IAC valve connector Fig. 5: The IAC valve is retained by two bolts Fig. 6: Remove the two IAC valve retaining bolts and... Fig. 7: ... remove the IAC valve from the intake manifold Fig. 8: Thoroughly clean the IAC valve mounting surfaces Fig. 9: Always use a new IAC valve gasket when installing the IAC valve onto the intake manifold