Looked through archives but did not find anything conclusive, when I just fire up the engine on cold the idle is around 470, when the engine wormed up idle is at normal 550...
I also have occasional ABS light on

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1987 300D
2005 E320 CDI

as similar problem with the cold idle, but no ABS light. I will be watching this thread for info.

First thing to check is the OVP relay. Is the fuse intact? Does the relay rattle like something's loose inside? I don't know how to check it other than to plug in a new or known good OVP relay. Some folks tear into it and find bad solder joints.

Forgot to mention - move the ELR knob to a numerically higher setting (note the original setting). If idle increases, EDS/ELR is doing it's job though with questionable effect if idle is low. If that changes nothing, EDS/ELR is not communicating with the IP.

Sixto
87 300D

Moved the knob to a higher setting without any affect on the idle, so does this mean ELR is bad?
Not really sure where the OVP relay is, anyone has a pic of it?

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1987 300D
2005 E320 CDI

It's in the cave behind the battery.

Picture pilfered from Fastlane.

Sixto
87 300D

Attached Thumbnails

 

EDS or ELR failure is uncommon. OVP relay and bad wiring/connections are the usual suspects.

Sixto
87 300D

Thanks for the pic, I will start from there!
Probably just order this part and replace it then report the results.

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1987 300D
2005 E320 CDI

A flaky or failed OVP relay or its built-in fuse will prevent both the EDS (Electronic Diesel System) and the ABS system from working correctly, according to the ETM (Electrical testing Manual) page 115 and 148. That could account for your low idle speed and your occasional ABS light.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Bingo!
http://www.***************/search/product.aspx?sid=zqpsmjvu0eztzu454pykmqjx&makeid=800016@Mercedes&modelid=1193802@300DT&year=1987&cid=18@Electrical%20%26%20Vacuum&gid=4593@Overload%20Protection%20Relay

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1987 300D
2005 E320 CDI

Some have reported success with resoldering the little circuit board in the OVP. This procedure has been shown to work for cold solder joints in the cruise control brain and ACC pushbutton unit but I have no personal experience with the OVP. Might be worth a try before spending money on a new one.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Be sure you plugged the airflow sensor (under the air filter box) back in if you had removed it.

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Gone to the dark side

- Jeff

Hmm, that's a good suggestion. I have not seen any sensors when replacing air filter.. anyone have a pic of that thing handy?

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1987 300D
2005 E320 CDI

It's the big aluminum assembly under the filter housing. I find it easier to work on the head and turbo with the aluminum heat-shield / inner-firewall removed from the passenger side of the engine bay, didn't know if you had done that and inadvertantly (or purposely) unplugged the airflow sensor. Give it the once-over looking for unplugged wires and such after surgery like that.

__________________

Gone to the dark side

- Jeff

I know folks have ripped out the MAF altogether with effect on idle control.

Sixto
87 300D