Idle Speed Fluctuates

Check Idle Air Control (IAC) valve. See DTC P1508 or P1519 in appropriate SELF-DIAGNOSTICS article.
On 3.5RL, check generator FR and A/C signals. See SYSTEM & COMPONENT TESTING article.
Check fast idle thermovalve. See SYSTEM & COMPONENT TESTING article.
Check idle speed adjustment. See ON-VEHICLE ADJUSTMENTS article.
Check throttle cable and throttle body for sticking and binding.