Can someone post an illustration of the location of the IDLE ADJUSTMENT SCREW/KNOB on a MB 420SEL/560SEL V8 motor? NOT THE CO adjustment of the fuel distributor but the screw to increase or decrease idle speed WITHOUT touching the fuel distributor CO adjustment.

I'm almost 100% certain it's electrically controlled. I just posted a thread regarding idle diagnosis in these engines; check it out and see if any fit your symptoms! Anything other than just high idling?

-Carlen

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1987 560SEL (210,000 miles)

^ What he said. There is a box that can fail on some models that will cause high idle, etc.

I could not even begin to guess where a manual adjustment would be. Adjusting the AF ratio does not change idle anyway.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

There is no manual adjustment, it is computer controlled with the idle control valve.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Also looking for a used and functioning Warm Up Regulator for no emissions gear Gen 1 Euro 500SEL Bosch part No. 0488 140 056 B 916 or MB part No. 116 700 362

No high idle or erratic idle; just low idle enough to want to stall car sometimes; recall seen a pic from a 126 manual showing a mechanical idle screw hidden somewhere low in the intake manifold?

I know there's a screw for the M103, and I think in earlier iterations of the M117 there was a screw on the warm up regulator, which was kicked once we went to electronic idle control... As to late M116/7, no such screw exists...

I think you might be the first to have a low idle problem

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1987 560SEL (210,000 miles)

Idle on my 500sec was low - ~500rpm - so I adjusted the throttle cable adjuster ( up to ~750-800) as a temp until I can look into it "someday". Mine is a euro so I don't know if others had this cable adjustment. It's a plastic threaded piece with nut near the end of the cable under the hood.

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85 300 SD ~ 115K
82 500 SEC Euro ??K
78 450SL 164K