My 93 300E 2.8 is exhibiting some symptoms that are similar to what some have described on here as a bad idle speed switch (as in the switch on the TB that is closed both at idle and WOT). Sometimes when I'm sitting at a light with the A/C on, the car wants to lurch ahead when the A/C kicks in and out. Also, it "hunts" (surges) while idling in park sometimes like it is not entering the idle program. However, I see no mention of a "switch" as such on my service manual CD for the 93 104 engine. Instead, it describes the idle being controlled by a number of parameters (coolant temp, MAF, etc.) though what they call the "electronic accelerator pedal", which I'm assuming is "fly by wire" arrangement on the TB. Can anyone confirm the presence or absence of a simple idle control switch on the 93 104 engine? Thanks.

Built into the throttle actuator.

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Thanks for the response, MB Doc. So, does that mean it can be tested? Is it a simple open/closed circuit switch type of thing, or is variable resistance affair whose resistance is interpreted by the control module? Just curious as to whether this might be the cause of my issue. Although it's only a minor annoyance, it doesn't seem right that it should try to lurch on me at a stop when the A/C kicks in unless my foot is relatively firm on the brake pedal.