The "Microswitch" is in the throttle linkage nest and should be easy to see with the air cleaner off.

The "Throttle Position Switch" is located at the end off the throttle butterfly valve shaft - opposite end as the linkage attachment - and is more difficult to see on most models. (And may require removing the fuel meter if you have to replace it. Thank you Mercedes for the great "maintenance engineering"!)

The microswitch tells the KE controller to interrupt fuel flow when you lift completely off the throttle (and there is about a two-second delay built into the controller electronics) and resumes fuel flow when you step back on the throttle. By resuming fuel flow before the throttle valve actually begins to open, the typical "jerkiness" of single switch systems is eliminated making the transition back to fuel flow seamless. And the fuel flow interruption delay eliminates any jerkiness if you quickly transition between off and on throttle multiple times in quick succession - what the tech literature on the system refers to as "hysteresis". ("Engineered like no other car in the world", remember!)

The TPS sends an idle signal to both the KE-Jetronic contoller and the EZL ignition module to tell the KE controller to go into idle speed control mode and the EZL to fix timing at the programmed idle speed setting (see emission decal for that setting.)

The TPS can get dirty/sticky and not send the idle signal, which will cause uncontolled high idle speed. This is often overlooked as a cause of high idle speed. (It's not always the OVP relay!) Often just a good exterior cleaning of the switch and shaft will restore function.

DO NOT DIDDLE WITH THE THROTTLE STOP ADJUSTMENT!!!

The TPS has three leads - idle signal, WOT signal, and common ground. Proper operation can be checked by disconnecting the TPS pigtail at the engine harness connector and checking these circuits with an ohmmeter while you move the throttle to idle and WOT. Trace up the pigtail up to locate the connector. IIRC the center wire is ground and the other two can be quickly determined by testing for the idle and WOT continuity signals.

The microswitch is easy to check for mechanical and electrical function.

Duke

thanks for the reply Duke. Im chasing down a stalling problem while I am idling at a stop sign or coasting. But again, my real question was if there exists a throttle microswith on a 126 engine. I have already cleaned the butterfly valve and R &R the TPS. But,I do not see a microswitch on my throttle linkage and Fast Lane does not offer one for an 87 420SEL. Yet, many posters have said it exists for THEIR cars, yet no posts have specifcally said it exists on their '87 420. I had come to the conclusion that my engine does not have one.

Hello Duke.

You are absolutely right one should never touch that stop.

I made the mistake to unscrew the throtle stop adjustment on my car w124, 260E, 1988.

Since it is a nightmare for me to get it back to the right position.
Have you any idea about the adjustment method, or should it be done only by MB dealer or Bosch specialist to have it adjusted.

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Keep us posted especially if your problem is solved
Present cars:
My car: E-class 420CDI, 2008, W211, V8, 180 000km

Wife's one: C-class 220CDI Sport Coupé, Euro, 2002, W203. 345 000km

Son's one: GLK class, 220CDI, 2009, W204

Sold: E-class 260E, 1988, W124, Wonderfull car sold after 489 000 kilometres of reliable services (engine M103, clutch, brake system and 5 speed manual gear box all original).

Sold: E-class, 320CDI, W210, 2000, 225 000km