Idle Control Valve Question
 

Does anyone knows if the "door" of the valve
should be completely shut-closed when closed,
of slightly opened ?

After I cleaned ours (1991 190E 2.3), I noted its movement was free all the way to the stop, where it remained open a slight amount. I was satisfied it was stopped mechanically at this point, and the opening was still sufficient that any slight wear would not have made any difference.

I tested it with a bench power supply, so I could adjust the voltage/current supplied it, and it appeared to react smoothly, consistently, to the applied voltage on its terminals. Testing prior to cleaning revealed a certain gumminess to its action, and repeatability was not so good. Since this device is inside loop control for the idle speed, I suspect the engine controls can recover from most ills of this device other than jamming, failed electromagnet, or air leakage.

Steve

Different answers for different cars.

Basically the idle valve goes to a limp home position when unpowered. Again this varies by system. The system used on 4 and 6 cylinder KE aquires an opening size that gives an amount of air equal to a slightly higher than normal idle speed with the A/C off and out of gear. That same amount is not very good when the A/C is engaged and the car placed in gear.

The early K-jet w/Lambda v8s had valves that went all the way open when unpowered.

The LH, HFM, and ME systems use throttle aactuators that are spring loaded to a position similar in concept to the KE cars (slightly higher when unpowered).

the reason for this question is due to some maintenance
(cleaning) suggested by some listers, which include
bench-testing the unit with 12v power.

thanks, steve b. for clarifying this.