Look at it this way - if removing electrical input to the ICV allows a smooth idle at a consistent rpm, then mechnically it is returning properly to rest. Also, it likely is operating smoothly around that point as well.

The ICV is controlled by the idle control circuit of the ECU, and any of several inputs to the ECU can tell it it needs to modify the position of the ICV. This is causing your variable idle, and some sensor is probably the culprit, or the sensor is properly reading an incorrect condition, and the ECU is trying to compensate by varying the idle. Either way, I would look at the input sensors:

-temp sensors
-oxygen sensor
-air flow meter potentiometer

etc.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7