Okay, perhaps a stupid question, but my w124 idles fine, but I am always trying to learn more about the car. So I adjusted the ELR adjuster (sorry if it has a better name) by pulling it out and turning. It was able to be turned in either direction without any stops. In other words, it could just spin and spin in either direction. And it didn't do anything to the idle of the car.

So I know it has 7 or 8 settings, but as you turn it, does it stop at each setting or is it a continuously smooth adjuster? Can it be turned more than 360 degrees? To get a change in the idle, do you have to re-engage the knob to its normal position, or should the idle change as you are adjusting it without necessarily re-engaging it into its locked position?

Someday I want to get this system working again and I know it has several parts. But I thought I would start with the adjuster, because its behavior just didn't seem normal to me. Thanks for your time.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

You need to turn it then push it in to engage the plug. Or you can remove the plug completely so u can see whats going on inside.

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CENSORED due to not family friendly words

There is a set of resistors inside the plug. Pulling out the plug, lining it up with another number, and pushing it back in puts different resistance values in the control line to the EDS box. This resistance value is used by the EDS box electronics to establish the baseline idle speed.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Thanks guys for the help. I mistakenly assumed it was some sort of rheostat, which a continuous change of resistance. But because it has 7 discrete values and you need to re-engage it to determine any change, I need to go back and check it again. I also didn't realize it just popped off. So thank you.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).