Idle Air Control Valve Not Getting Ground to Opening

I have traced my cold start problem to the idle air control valve which appears not to be getting the proper voltage control signal from the FI ECU.
Unplugging the connector to the idle control valve results in no change to idle. If I apply 12v and ground to the valve (electrical connector off), it clicks open and idle increases. Based on this, I think the valve is ok.
There is 12v on the left prong of the electrical connector with the ignition on. The right prong of the connector is a very weak ground.
It appears to me that idle air control valve operation is controlled by ground resistance at the FI ECU. I am guessing that the ECU varies ground for the idle valve depending on reports from other sensors in order to increase or decrease idle.
The coolant temperature sensor appears to be operating within range. The over voltage protection relay is new looking and the fuse is intact.
I am not sure what to do now. Should I replace the computer and see if that solves the problem? Is there another sensor besides the coolant temperature sensor which could be causing a problem with the control operation of the idle valve?
To recap my symptoms, the car was not starting well at all when cold. Even when warm, idle seemed not quite right. On occasion, the car would start well cold, which led me to conclude the problem is an intermittent electrical fault.
Thanks,
Robert
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Sorry, It's a 1987 300E (W124). Motor is 103.983.

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On Wed, 10 Nov 2004 16:55:00 GMT, 9kman wrote:

The Haynes says about this system (Bosch CIS-E (KE-Jetronic)):
"A thermo-time switch controls the amount of time the cold start valve remains open. The auxiliary air device is a valve which allows air to bypass the throttle valve, hence raising the idle speed. A (sic) internal bi-metallic strip and heater coil controls both the amount of valve opening and length of time for which it remains open."
This suggests to me that this unit is independant of the ECU. It seems to be an electro-mechanical timing device that just gets on with one small task in a larger system. At least, that's how I read it, what does everyone else think? Mike
--
W126 300SE 234,000 Miles
W115 220
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Mike,
Thanks for the reply. I think the auxiliary air valve is different than the idle air control valve. Does Haynes say what controls the idle air control valve?
Thanks,
Robert

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On Thu, 11 Nov 2004 14:08:05 GMT, 9kman wrote:

Can't see that, but it does say this:
"Later variants are fitted with a rotary idle actuator. This componant replaces the auxillary air device and is driven electronically by the ECU. It provides engine idle speed stabilisation during all operating conditions, including fast idle during warm-up, and idle speed control under load, e.g. when the power steering, or air conditioning are actuated."
It also lists these:
Coolant Temp Sensor ================-Type: NTC -- Electrical Resistance -- @ 80C 325 ohms -- @ 40C 1200 ohms -- @ 0C 6000 ohms
Thermo-time Switch ===============Heater Coil Electrical Resistance 93 ohms Duration (length of time contacts are closed) -- @ -20C 12 seconds -- @ 0C 1.5 seconds -- @ 3C 0.5 seconds
Air Flow Sensor Potentiometer =======================Supply Voltage 7.0 - 9.0 v Wiper Voltage Variation -- Engine Off 0.25 - 0.5 v -- Full Scale Deflection 7.0 - 9.0 v
I hope this is some use to you. Mike
--
W126 300SE 234,000 Miles
W115 220
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Tugging back and forth on the computer has temporarily solved my problem. Therefore, I think the problem is either a break inside the computer or a loose wire in the harness. It's now working correctly so I will have to wait for it to malfunction again to fully isolate the cause. I did take the computer out of the case and it looks fine.
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Double check your sensors. You said..."I checked it tonight with the motor stone cold at 30F and the resistance was 5,000 ohms."
Rating according to Mike is 6000 ohm at 0 degree C... so you are 1000 ohm off... this is huge. Like I told you in the first place.
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