I'm needing to raise the idle RPM a bit on my 260E. Anyone have a pic or a link that shows where this screw is located? Is it a 3mm hex?

Thanks
Dale

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Dale

IIRC idle is computer controlled. If it isn’t right, check for vacuum leaks and idle mixture setting.

Sixto
98 E320s sedan and wagon
02 C320 wagon

On an '88? I didn't think there was much that was computer controlled until a few years later. I may be sorely mistaken though

Dale

EDIT: I made a 1/4 turn CW (rich) on the EHA today and it made A TREMENDOUS difference in the way the car accelerates and starts! But now the idle is a hair too low - approx 500-600 RPM, sometimes it may fall below 500 briefly then come back up.

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Dale

M103 idle speed is definitely controlled by the "e-part" of the KE system. There may be an initial adjustment, but I've never messed with it.

The initial mixture adjustment should be done by measuring the duty cycle and adjust if necessary. A search should yield many threads on the subject.

Since idle speed and cold start enhancements are controlled by the electronic unit that is supplied power by the OVP relay, a dead OVP relay will cause hard cold starting and idle speed problems. If the ABS light is on there is likely a problem with the OVP relay as it also provides power to the ABS electronics.

Duke

NT

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Dale

Agreed. That’s probably why California directed my ‘91 300SE to gross polluter smog stations even if it never failed a test. The M103 is a frustrating beast to tune when the fuel system starts to wear.

Sixto
98 E320s sedan and wagon
02 C320 wagon

Indeed they are! I've finally started seeing light at the end of the proverbial tunnel with mine though. It basically starts well, runs well, and now after that very small tweak of the EHA, the acceleration from dead-stop is better than I've experienced since owning it!

There's a guy from Australia I think it is, on YouTube (goes by MMWA) that I tend to watch his 'journey' with his later model W124 (92 or 93, maybe) and he has a video taping about the EHA adjustment and what a remarkable difference it has made for his car. And I believe in it he mentions a "3mm hex screw" idle speed adjustment that may or may not need to be tweaked after one makes the EHA adjustment. I'll have to go back and find that video to see if he actually shows where it is located. All I know at the moment is, my car idles very smoothly now, albeit a little slower, and acceleration is remarkably improved

Dale

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Dale

IIRC the adjustment screw accessed through the air cleaner is for idle mixture, not idle speed. It might change idle speed but that’s not what it’s for.

Sixto
98 E320s sedan and wagon
02 C320 wagon

Yes, that's my understanding as well...

I am going to leave things as they are since it's not THAT bad. Not sure if a low idle speed can cause spark plug fouling or not but if it starts running ragged I'll have to do something at that point.

Dale

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Dale

Pierre Hedary has a good video on his Youtube channel on the EHA found here:
https://www.youtube.com/watch?v=XclGM2RgDDo
Many good videos on older Mercs. He is an MB fanatic!

Thanks rob300e, I follow him as well and have actually seen that video and it may be the one I have seen that mentions this illusive idle screw! So, thanks for posting it.

Yes, Pierre is a gem where these old Benz are concerned!

Dale

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Dale

That is actually one video I have seen that mentions this "3mm screw..." but Pierre doesn't disclose its location. Wondering if it is the one that is accessed from atop the air cleaner housing....? If anyone knows please let me know. Thank you

Dale

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Dale

The 3mm screw adjusts the main mixture, not the idle speed. Your idle speed should be electronically governed.

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It 'should'? If that's true, then it's not working. While the overall performance has been radically improved by the tiny adjustment to the EHA, the idle is maybe 200 rpm too low. THAT is what I'm trying to fix.

Dale

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Dale

Where is your idle speed at now?

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).