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Dan,
Noel is very thorough in understanding and explaining that valve. I agree, in thinking the base idle set operation of the idle valve does not shut it down, but sets the duty cycle at a fixed point, like you said, one that allows the widest range of correction by the ECU. Probably pretty close to a midpoint for flow.
Also, I believe its vibration does not have much amplitude. What I mean, is the mass of the armature and valve assembly don't allow for it to open or close very much in either of the two phases. So its operation may be infinitely variable between open and closed, but instead of drawing the huge currents an analog servo would require, the motion is done binary fashion with much less electricity and heat.
I do know the two coils are alternately grounded by the ecu pins 10 and 23. One always has the opposing polarity from the other. This in itself would make it reasonable to guess it never stands still as long as the main relay supplies current to the center terminal of the valve (and the ecu is working!), so I guess you may not see a change when you use the test point, under certain conditions.
My experience with LH2.0, which apparently uses a different test point to set base idle, on pin 15, is the idle may or may not change when you connect the ground to the test point, but it always jumps up and settles when the test point is released and feedback takes over. Can't claim any LH2.2 experience.
(It was decided the wife's 89 245 won those beautiful corners, btw.)
--
Art Benstein near Baltimore
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