usually is the TB gasket, IM gasket, or IACV when the top is plugged
When the engine has a high, hunting idle, pull off the intake and look into the throttle body opening where air flows. You will see two holes or ports on the inside wall of the throttle body. The upper port leads to the MAP sensor whereas the lower port leads to the IACV. Cover the IACV port with your finger. If the idle speed drops and fluctuation stops, then try to adjust the idle screw on the throttle body. If this doesn't work, then the IACV, ECT sensor, or TPS may be bad. If covering the IACV port does not affect the idle speed, there is a vacuum or intake air leak.
All vacuum hoses connect to nozzles on the intake manifold. Disconnect each hose one at a time and then cover the corresponding nozzle with your finger. If the idle speed drops to normal for any disconnected vacuum hose, there is a leak in that hose system.
If there are no vacuum leaks, then the throttle body or intake manifold gaskets/bolt torque should be considered next.