The best way to view the control of the idle valve is with duty cycle or current in milliamps. Typical current will range from 6-900ma. Duty cycle is actually the best view if the car is idling too high. The system will crank out a maximum of around 70% ON duty cycle trying to close the valve. If the speed is high and the duty cycle is at 70% either the valve can't close far enough or air is entering the motor somewhere wrong.

If you loose all voltage when the valve is connected I would look at the OVP for source voltage. Loosing the voltage like that is an indicator of a weak circuit. one that won't hold the load. The load should be able to hit 900ma trying to close the valve.

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