I am shooting this problem and have now focused on the idle speed air valve area of the EM system. I have been thru the archvies and recall hearing that at idle when one removes the two pin connector on the idle air vale (which is connected to the idle speed controller) that the idle speed should increase. This does not happen in my case.

I have measure the following in relation --
-resistancs is perfect - 3-5 ohms.
-At idle the voltage accross the terminals is 1.25 volts and does not change or vary with rpm or engine temp.
-the MB engine manual has a test defined that looks at current thru this component and look for 700-1000 ma -- can this be possible???? A full amp of current thru these flimsy 14 ga wires???

At any rate - by my caclulations if the resistance is 3.5 ohms or so and the voltags is 1.25 volts -- the resulting current is about 300 ma or so and substantially under spec.

I have put this idle air valve on the bench and put 12v accross the terminals and noted the audible clicking expected.

Am I chasing a goose here???

FYI- my symtoms are long cranking when cold, very rough and slow idle to start until the air pump cuts out and/or something else changes and the idle smooths out. At high speed the car runs fine and does not smoke or miss.

Thanks.

what year and model

__________________
dloveless

1984 500 SEL [131K]-
1991 GMC Sierra 4X4 XC [162K]- War Pony.
2004 Jeep Liberty Limited [8k]- wife's sled- Belle.

sorry - model is 560SEL 1986 vintage. --USA model.

Thanks.

not in front of my book but I believe mine is supposed to be "battery voltage" (approx. 12.5 volts) across that plug when key is on and engine off. Engine has to be cold I think also. I would check the tightness and cleanliness of the plug that the Idle control module plugs into between the two firewalls. I just experienced that problem and it was a real gremlin for me. Again, not sure if your 86 560 is same as mine but I think they are very similar on this part of the car. The test for the ICV was listening for the audible click when turning key on but the buzzer was too loud on mine and could not test it that way so I turned the key on waited for buzzer to go silent and plugged and unplugged the Idle control valve and cold hear click then. I thnk your problem is either in the ICV [idle speed air valve]or the Idle control module.

Good luck.

__________________
dloveless

1984 500 SEL [131K]-
1991 GMC Sierra 4X4 XC [162K]- War Pony.
2004 Jeep Liberty Limited [8k]- wife's sled- Belle.

ALGAE, I WOULD REMOVE THE INJECTORS AND DO AND BENCH TEST WITH THE INJECTOR TESTER. IF ITS A 116-117 ENG THOSE ARE KNOWN FOR INJECTORS AND INJECTOR SEATS.
GOODLUCK

Well i did do the injectors as a replacement early on to attempt to resolve this problem. I didnt see any difference in the idle problem. I have observed the following :
-the voltage "open loop" when i remove the ICV from the ICU circuit is unstable and moving around 1.25 volts.
-when i remove the connector from the ICV with the engine running there is no idle difference.
-When i turn on the compressor there is noticeble DECREASE in idle speed from about 800 to 550 rpm indicated.
-With KOEO the voltage at the ICV is 1.25 volts and i cannot hear the classic click.

I am starting to conclude the ICU is bad or at least a very bad actor. Is there any further way I can reconcil the ICU vs the ICV???How about removing the connector from the ICV once the engine is started and put battery voltage on it to see if that chnges the idle???

Thanks.