and the ECU takes a few seconds to reduce the pulse rate to the idle air valve and pull the idle down. But the IAV can only reduce the idle by so much. Unplug the IAV from the harness and see if the RPM remains at your 1.5-2K range and does not settle down. If so, see if you can manually reduce the idle via the IAV idle speed screw... if you can't, you definitely have a vacuum leak or the throttle valves are open too far. To check for vacuum leaks, spray starter fluid around all the plenum gasket surfaces and vacuum ports while the engine is idling to see if you can find a location that makes the idle speed change.
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