Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help

Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Diesel Discussion

LinkBack Thread Tools Display Modes
Old 01-31-2008, 01:16 AM
Registered User
Join Date: Nov 2007
Location: Vancouver, BC
Posts: 173
617.952 idle speed question

Hi guys,

First off - a preemptive thanks to anyone who can answer this simpleton of a question (I hope). Lately (in the last 2 months) I've notice my idle speed immediately after starting seems too low.

The case used to be that I'd start the car (it lives in a warm underground garage) and the idle would be 750 rpm almost exactly (whether the engine was cold or not). Nowadays, the engine starts up and it's 500. It doesn't quite /sound/ like it idles at 500 to my ears, and certainly the idle does not feel any rougher than when it used to read 750, but 500 is what my tach is telling me.

If I go on to drive a few blocks, the idle "usually" will seem to reset itself and sit at 750. Sometimes 600, 650 but 99% of the time, after a reasonable 15 minutes of driving, the idle behaves itself and sits at 750 or thereabouts.

Should I try to do anything about this? I doubt it's having any immediate negative impact on my motor... but, perhaps I am wrong. Could this be a linkage issue? maybe there is a screw I can adjust manually? Seems like a good weekend project, but some ideas on where to start would be most appreciated. Seems like some other 300DT owners on this forum have had similar symptoms...

1984 300D Turbo, 326000 Km, Thistle Green Metallic
Reply With Quote
Old 01-31-2008, 01:29 AM
pawoSD's Avatar
Join Date: Oct 2004
Location: Grand Rapids, MI
Posts: 15,323
The tach's on these cars are not all that accurate. The degree of accuracy is about +/- 200 rpm. Its 99.9% likely the engine is still idling at the same speed as before....the tach is probably just "slow to react" sometimes....and they do seem to "reset" themselves after you've begun driving. Ours does it too. I'd not worry about it....just old electronics acting up.
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 90k - mine - (OC-91,200)
'17 Metris(VITO!) - 18k - wifes (OC-25k)
'01 E320 Wagon - 161k - mine (OC-165,000)
'01 E320 - 180k - dad's (OC-182,500)
'07 E350 Wagon - 134k - dad's (OC-139,500)
'01 SL500 - 56k - dad's (OC-59,000)
'16 E400 4matic Sedan - 81k - Brothers (OC-88,000)
Reply With Quote
Old 01-31-2008, 01:33 AM
Registered User
Join Date: Nov 2007
Location: Vancouver, BC
Posts: 173
That was my other thought - maybe it's just the tach being 24 years old.

That said, how is the tach actually coupled in to the motor - correct me if I am wrong but I have this idea in my head that it's a magnetic coupling to the transmission bell housing. I wonder if there is any value in cleaning / reseting that?

What is more likely is I will continue to live with it and all will be well
1984 300D Turbo, 326000 Km, Thistle Green Metallic
Reply With Quote
Old 01-31-2008, 01:52 AM
Registered User
Join Date: Oct 2006
Location: Boca Raton / NYC
Posts: 338
OK, Besides the tach being off, is there a way to adjust the idle?
I'd like to raise my idle about 200 rpm or so (for the winter months)
Reply With Quote
Old 01-31-2008, 05:36 AM
toomany MBZ's Avatar
Registered User
Join Date: Nov 2006
Location: central Va
Posts: 7,820
xdjio, I don't know where the sensor is on an '84, and cannot trouble shoot. Bound to be an electrical connection somewhere that may be the culprit.

AIRNUTS, in the pic it says to detach connecting rod 2, I did not do that, otherwise I can attest, this is how the idle is adjusted. You'll need a deep socket to loosen the lock nut in order to be able to turn the screw.
Attached Thumbnails
617.952 idle speed question-info-017.jpg  

83 SD

84 CD
Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

All times are GMT -4. The time now is 02:30 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page