The actual control of the idle valve is a pulsed battery voltage. When you read a 50% duty cycle pulse with a volt meter on a 12v circuit you get 6v. It is my recollection that these devices will only go to 70% duty cycle in attempts to control. That would be 8.4v if you measure it that way.

Obviously the best control would have the nominal condition somewhere in an easy control band. Thus I would have to guess you are right about the required voltages as I would guess 50% duty cycle is the middle.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician