[wayner]

[QUOTE=masraum;8741338]Well, when you put the car in drive (vs N) that puts a slight load on the engine which usually also makes the idle drop. I think there's supposed to be a solenoid that bumps the idle up a bit

Depending on the year, these things are all computer now not solenoids. At idles it uses one program. When it senses the throttle position movement (TP sensor), it switches to another program.THe idle program tries to keep it at a set RPM regardless of load. As long as the TPS does not detect movement, the idle program balances airflow, fuel, O2 exhaust etc. to keep it stable.

If there is an air leak, a dirty MAf sensor, a bad 02 sensor etc, it will hunt.