300 SD idle speed

The garage set up my idle speed too high, around 1,200 RPM. I understand it's supposed to be about 800 RPM. How may I change it without taking the car back to the shop at $90 an hour?
It just runs annoyingly fast at idle.
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Personally, I'd take it back to the shop and have them adjust it to the correct idle speed - about 750 rpm. They should do so (at no charge) as they somehow messed it up, maybe by bending the throttle linkage. Once YOU intervene their hands are clean, no matter what's wrong.
If YOU insist, there's an idle stop screw with a lock nut between the injection pump and the block - you'll need a deep 5/8 socket to loosen and tighten the lock nut and a long blade screw driver to turn the adjustment screw. However, I strongly urge you to first check that the throttle lever does, in fact rest against that stop screw at idle before doing anything in the way of adjustment.
Shops rarely adjust diesel idle speeds so its very doubtful that the idle stop adjustment is the cause but rather something in the linkage or idle controller if your motor has one of those (you didn't give its vintage).
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I had this same symptom happen to me once. The problem turned out to be that my drivers side motor mount had collapsed and the engine had settled (listed?) to the point where the linkage could not return to "normal". The mechanic I took it to showed me this on the lift (how embarrassing)
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That's not embarrassing, it just happened. Not something that you screwed up and then had to go, with your tail between your legs so to speak, to a shop and say "Oh, please fix MY mistake."
This owner paid for service and got service and then some. He ought to have that shop explain the discrepancy.
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What the hell kind of incompetant shop adjusts the idle on a diesel. You NEVER do that.
What problem were they trying to solve by doing this?
Worst case a new rack damper bolt and two cans of Diesel Purge fixes any diesel idle problems.
There's an idle adjustment screw on the IP, with a locknut. It's in the manual. My manual is packed away in a box. If you call the shop they should be able to tell you where it is.
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Thanks, guys. I will take it back to the shop. (It's a 1981 617, by the way). Seems that in the course of chnaging fluid and filters they also screwed up the transmission, which is now reluctant to upshift. Sigh. I just changed mechanics because the old one, who rebuilt this car and knows it thoroughly, moved his business thirty miles away. It takes an hour to drive there on a good day but getting home by train, bus and subway is another two hours. As Brooklyn boys dating Bronx girls used to say (maybe they still do) he became GU -- Geographically Undesirable.
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Yeah they still say that. But your mechanic is like my girlfriend. Worth the travel time.
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Richard Sexton | Mercedes stuff: http://mbz.org
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Nothing wrong with the new guy. Indeeed, he once worked for the old guy's father. But his pricing seems arbitrary and I don't feel as confident with him.

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Sounds like a vacuum hose got loose since it also affected your tranny.
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You will need a very long, deep well 14mm socket to loosen the lock nut on the adjustment screw. It is a pretty straightforward job. The idle adjust is between the injection pump and the block/head of the engine.
I have had good luck just loosening the nut and then adjusting the idle and then retightening the nut. The screw seems to stay in place when I tighten the nut with a socket. A better choice of wrench might me some sort of special 14mm open end wrench that has a right angle bend near the end so you can hold the screw steady with a screwdriver when you tighten the nut.
It has been a long time since I have had to adjust that. I may have used an open end 14mm to get the nut sort of tight while holding the screw in place with a screwdriver and then used the socket to completely tighten the nut after that.
Here are some images of the screw and its placement:
http://inyopro.com/idle_screw.jpg
http://inyopro.com/idle_screw_placement.jpg
Gogarty wrote:

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