Throttle related question on my 93. It runs beautifully and no issues when warm. But when cold, I get what I can only attribute to a sticking throttle.

At cold start, it idles low, like when the EDS Is not controlling the throttle properly (I am getting a code reader device so that I can check out all the systems). And idles around 550 RPM for the first few minutes when cold. That’s not really a big issue to me as I can probably figure that out, the bigger concern is that when I hit the throttle it sticks. For example if I want to move the car and I might take this engine speed up to 1000 or 1500 RPM, it will stay up there after I take my foot off the throttle. If I am trying to maneuver the car, going backwards and forwards, the RPMs will shoot up over 2000 RPM.

Because everything is so tightly packed under the cowl in this car, it is hard to see what the issue might be. Again, it does not happen once the engine is slightly warm. I would think that if it was something gunked up, or dirty, that it would always be sluggish to return. But that’s not what I see. Any recommendations on how to diagnose and potentially fix this?

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

Perhaps it is better to call it an overshoot. Is the w140 drive by wire? I believe my father’s w210 was, but it had a 606 engine.

You can see a few things on this cold start. It starts at about the right RPM (~750-850), but after any user interaction, it settles too low (~550). That final throttle blip is the best example. I gave it a little pedal and it kept going to over 3000. Once the engine is warmer it doesn’t seem to do this.

https://youtu.be/MXt9yiNTHdY

What in there might be sluggish?

The engine is very clean, and I lubed the throttle points I could.

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

Not a drive by wire,when colder, joints and balls on throttle connection gets stiffer and starts to stick a bit.Solution is to remove intake and clean and lubricate ALL throttle linkage balljoints.

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Mercedes W140, S350TD, 95.
Mercedes W140, S350, 92.
Porsche 944, 86 N/A.
Porsche 944, 85 N/A automatic.
Porsche 944, 84 N/A.
Porsche 944, 83 N/A.
Opel GT, 73.
Toyota Supra MA61,84.

Or could be that the return spring of the throttle(located on the inside of injection pump when you look the pump from the head side you will see it) has lost its strength and can not return the throttle.But 99% you will solve a problem by lubricating joints.
P.S.You have bad one or more glow plugs that is why glow plug light come ON when the engine is running.And your idle is good when it should be when hot 550-650rpm,when cold should be 150-200rpm higher.

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Mercedes W140, S350TD, 95.
Mercedes W140, S350, 92.
Porsche 944, 86 N/A.
Porsche 944, 85 N/A automatic.
Porsche 944, 84 N/A.
Porsche 944, 83 N/A.
Opel GT, 73.
Toyota Supra MA61,84.

Hello,

Yes I know I have a bad glow plug, and need to check connections for EDS on the w140. I have a code reader box coming too.

I do see that it’s sluggish when cold. I’ve read the cruise control (sometimes functional) can get sluggish and affect the return of the throttle. Not sure if there’s a more sluggish element in there.

I’ll pull the intake. I need to do so anyway.

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

With the engine cold and off, try moving the linkages by hand under the hood. See if it returns to the stop easily.

The idle speed being wrong might be a bad ECU temp sensor? Or other fault. The blink codes might be helpful.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000).

Tesla Model 3. 136,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

It’s definitely the cruise control. That little arm is very restrictive. TBD if lubing will help it to return.



The idle like that is consistent with the 3.5L OM603 in my w126 when the EDS is disconnected… I need to check for clean connections. I do have a code reader box coming….

Cruise worked once when I tried it. May try to lube it up but won’t hold my breath. I wonder if the linkages can be reinstalled without removing the intake??

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)