The idle speed is controlled by the computer and cannot be adjusted.
You should remove and clean the Idle Air Control (IAC) solenoid.
While it is off (even before you clean it, use an ohmmeter to check its resistance (listed below): Turn the ignition switch to the OFF position.
2. Disengage the wiring harness connector from the IAC valve.
3. Using an ohmmeter, measure the resistance between the terminals of the valve.
If the resistance is not 7-13 ohms, replace the IAC valve.