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There are several things that can cause this issue,
Idle Air Control (IAC) solenoid.Vacuum routing issueProblem with the crankcase ventilation system
Disconnect the Idle Air Control (IAC) solenoid electrical connector to verify that the idle stays high, or drops to a low value, which will indicate if the idle is high due to Powertrain Control Module (PCM) influence. If the RPM is still high, inspect for a possible vacuum leak related to the crankcase ventilation system or misrouted vacuum hoses. Remove the Idle Air Control (IAC) solenoid and block the holes with tape to see if the idle is still high or drops, indicating that the IAC solenoid is defective.