A little misconception regarding function of idle control valve.

Whenever a cold engine is started it requires a rich mixture and a little more than normal throttle opening to keep running.

On carb cars, there was the choke blade and the fast idle cam.

On FI cars, there's the extra injector or a computer program to create rich running and there's the idle control valve to bypass a little more air, i.e. creating same effect as a fast idle cam but not actually opening the normal throttle blade. These are both controlled/monitored by an engine temperature sensor input to computer.

Not much action from idle control valve once engine's warmed up, except that it's supposed to be closed. It indeed "controls idle" during engine warmup, but after that it doesn't do anything.

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles

In the mornings when my engine is cold...for about 5-10 seconds I do not have a misfire then it slowly gets worse for the next 10 seconds before it feels the same as when it is warm. Could there be a possibility that the valve is not closing when it should be? Would that be considered a vacuum leak? (I have had the car smoke tested and I have no visible vacuum leaks at all.

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If the valve was not closing then you'd just have a high (but not misfiring) idle....around 1500ish....

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