Is there a throttle microswitch on my 87 420SEL? If so, where is it located?

Thanks

Idle contact/full load is located on the throttle butterfly.

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can you get more specific on what Im looking for? with the airfilter housing removed, I see the throttle linkage and I dont see any type of a switch connectted to the linkage. there is a pic of a microswitch that Ive attached listed in the parts section but its for a 87' 300t. Am i looking for something similair to this?

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Here is a photo.

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78 Corvette Stingray - 3k
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Thanks dpetryk! I understand now. I thought that there was a microswitch AND a throttle switch that I needed to troubleshoot and I was tearing my hair out loooking for the microswitch!

The 103 engine does have both those switches.

The 420 does not?

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the throttle microswitch (gray) shuts off fuel on the m103 after you take your foot off the pedal, if I remember correctly.

What problem are you chasing?

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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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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

HUGE thanks for the picture from me. I'd given up looking and concluded that this '89 w126 500SE didn't have such a switch at all. Which was a damn shame because the engine behaviour suggested that if there was one, it wasn't working.

Now, thanks to you, I've found the stoopid thing - and it isn't working!

Well, it's intermittent: it operates if you let the butterfly snap shut, but letting it close gently usually doesn't close the contact.

My question now - before I go burrowing into the engine to get my hands on it - is what am I in for if this can't be resurrected? Do I have to replace the entire Throttle Body, or can I get the switch separately?

Anyone have a clue? I'd be very grateful for any info.

CD

OK, I went hunting through the catalog, and found P# C7010-76651, which looks just the business. I'm very interested to note that the switch seems to have elongated screw holes to allow for a few degrees of adjustment, and I'll see if I can slacken the screws and wiggle the existing one first.

CD