[sas95]

OK, think I've experimented with this thing long enough. Even though the repair manual says the IDLE SWITCH parameter should be ON during what it describes as specific idle conditions - idle/upper radiator hose hot/closed throttle/park/neutral/closed loop/accessories off, the IDLE SWITCH is OFF in these conditions on my car. Only when I turn on the A/C will the IDLE SWITCH parameter go ON. The ISC motor then extends its plunger to contact the magnet screw, and moves the throttle up from 1.5 degrees to 2.9 degrees (todays conditions) to keep the rpm around 890. With A/C turned off, the ISC probe retracks away from the magnet. I notice that the ECM is controlling rpm in this situation, but probably through other means, possibly injection pulse width, timing. After I turn off the A/C, the engine rpm goes from 890 up to 1300, then down to 1100. All this without me touching the gas pedal.

Think I'm doing to leave the whole thing alone.

The reason why I've been diving into this is the manual says that when diagnosing a DTC,

1st - do an On-Board Diagnotic system check using a Tech I scanner, so that you can trust the ECM,

2nd - verify the 26 parameters coming from the ECM with a Tech I scanner are within expected bounds,

3rd - follow the fault isolation chart for the specific DTC you've got

If any of the 26 parameters are not within bounds, you're supposed to keep this in mind when in getting to the bottom of your DTCs.