My chevy 3.1L V6 95 engine recently has high-idle RPM ( about 1500), which last unusually long time, after the engine got first started in the morning after an over-night park. After that, the idling RPM seems fine.
Prior to this, the first start-up idle RPM sometimes fast settled to normal RPM, but sometimes slower. The IAC valve's terminal resistances has been checked okay according to a specification. And the morning temperature has not varied much! Your feedback is appreciated!