Was it just to make the car seem more modern and appealing to the uninformed driver? It wasn't an NA/Turbo change since the 116's with the 617 turbos still had manual idle control.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

i'm guessing that there was a change to the idle governor inside the injection pump which made the external control unnecessary. did the transition occur at the same time they went from ADA to ALDA pressure sensing devices?

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'77 240D, 504H, OM617.952, etc.

I don't think so. I'm pretty sure the 116 turbos had an alda.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

FWIW The IPs changed to vacuum fast idle long after W123 production ceased.
However the 616 and 617 were still sold in vehicles into the 1990s, I don't know if they had the idle knobs or not though!

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1978 300D, 373,000km 617.912, 711.113 5 speed, 7.5mm superpump, HX30W turbo...many, many years in the making....
1977 280> 300D - 500,000km+ (to be sold...)
1984 240TD>300TD 121,000 miles, *gone*
1977 250 parts car
1988 Toyota Corona 2.0D *gone*
1975 FJ45>HJ45
1981 200>240D (to be sold...)
1999 Hyundai Lantra 1.6 *gone*
1980s Lansing Bagnall FOER 5.2 Forklift (the Mk2 engine hoist)
2001 Holden Rodeo 4JB1T 2WD

I think it's because most people broke the knobs off them...it's difficult to turn the knob when the throttle is in the normal idle position.

It's more accurately a pre-start-of-engine idle adjustment knob.
With the car off, you step on the accelerator pedal to move the throttle linkage, taking strain off the bowden cable...then you turn the idle adjustment knob to shorten the bowden cable...thus enriching the idle when you finally start the car.

You couldn't speed up the idle with the knob while the car was already running...unless you simultaneously feathered the accelerator pedal just the right amount.

It wasn't a "fool"-proof system.
And..who reads the instruction manual anyway?

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

I never knew all that! The knob on my 1978 car just freewheels, and I never bother to fix it or even investigate it further. In my defense, I do not have an owners manual for this car, although perhaps I should get one, if it explains things like that.

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2007 Dodge Ram 3500 Cummins Turbo Diesel 4x4
1994 GMC S-15 pickup 4.3 5MT
1985 300 SD
1978 300 CD
1962 220-S Fintail - awaiting restoration

It is hard to say what motivates Mercedes to do stuff. However, the dash does look cleaner without the knob.


I have not seen any Diesel Vehicle that has such an idle control device on it except possible Boats. Other Diesel Cars don't seem to have them and don't appear to need them.


My Volvo had a thermostatically controlled gizmo for cold starting connected to the coolant.

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84 300D, 82 Volvo 244Gl Diesel

My Fuso has a manual idle speed control. So did the CAT 3208 in my Wanderlodge.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I imagine they got rid of it because it was a cost to include for a device that was widely misunderstood and used wrongly or not at all.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I'm wondering if USA regs changed and prohibited hand throttle on a car. ( as in it being used as cruise control, if it goes that high )

It won't go that high, its just a manual fast idle.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

The merc ones did if you had it set up right (or wrong, lol)
The old Mitsi/ Fuso Canter I used to drive had one, same with D21 Navara, etc

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1978 300D, 373,000km 617.912, 711.113 5 speed, 7.5mm superpump, HX30W turbo...many, many years in the making....
1977 280> 300D - 500,000km+ (to be sold...)
1984 240TD>300TD 121,000 miles, *gone*
1977 250 parts car
1988 Toyota Corona 2.0D *gone*
1975 FJ45>HJ45
1981 200>240D (to be sold...)
1999 Hyundai Lantra 1.6 *gone*
1980s Lansing Bagnall FOER 5.2 Forklift (the Mk2 engine hoist)
2001 Holden Rodeo 4JB1T 2WD