Idle Speed Fluctuates

Check Idle Air Control (IAC) valve. See DTC P1508 or P1519 in the TESTS W/CODES - GS-R article.
Check fast idle thermo valve. See procedures in the SYSTEM/COMPONENT TESTS - GS-R article.
Check idle speed adjustment. See ADJUSTMENTS - GS-R article.
Check throttle cable and then throttle body for sticking and binding.