No fast idle on '91 190e 2.3
 

My car ('91 190e 2.3) always idles around 750RPM no matter whether it's a hot or cold start. Shouldn't it have a faster idle on a cold start? What should I look for? It idles perfectly other than the no fast idle on cold start.

-irieite

Idle speed is controlled by the ECU. When cold, the engine will be supplied with more fuel and air, but only enough to maintain the correct idle speed (ie. the same idle speed as when hot). Yours is functioning as it should. This system allows correct idle speed even with varying loads such as air conditioning cycling on and off. In my manual 190E I can even engage first (or reverse gear) and ease the clutch out and have the idle speed remain constant such that the car will drive at idle speed without touching the throttle. It will even reverse up the moderate slope of my driveway at 750RPM by way of the idle speed control.

Thanks for the info. I guess it's good to hear something on my car is functioning as it should. ;)

On our '91 190E, the car always idles at 1200 rpm when started cold. After less than a minute, it drops back to 750 and stays there.

Steve

After reading Steve's comment that his idles at 1200 after a cold start, I checked mine again. Cold idle may be marginally faster, say 850 to 900. Hot it sits at about 750 to 800. Hot and cold the idle is smooth, probably slightly smoother cold.

My car starts right up when cold, but it kinda stumbles at first and actually idles around 500 immediately after start up. After I hit the gas to bring the revs up for a few seconds, it'll idle around 750 after that..

-irieite

There is an engine temperature sensor that tells the ECU to go to fast idle on startup. There is also a cold-start valve that enrichens the mixture for a brief while on startup. Either could be malfunctioning.

Steve