PeachParts Mercedes-Benz Forum - View Single Post - New 1981 300SD Not a cream puff after all

Zacharias · #15 01-06-2012, 01:32 PM

You should put on the proper cigar hose (not expensive), but lack of it isn't causing the problem you're seeing now.

Nothing is going to self-destruct here.

The rack damper bolt isn't just a matter of changing it. The bolt has to be adjusted by loosening the locknut then tightening the bolt all the way in, then VERY slowly turning it back out until you get a smooth idle. Some cars can drive you nuts with back and forth before you get it JUST so. Others seem to be more forgiving.

If you can't get it smooth at your current idle setting, experiment with it.

Adjusting the bolt for a smooth idle has to be done with the engine HOT (I was taught that you ideally need to do it within 10 minutes of a good, high-speed run) and it works in conjunction with the idle speed setting.

Not every OM617 can be adjusted to a smooth idle at the same idle speed. Some are easier to set than others, and faster idle speed won't necessarily get you a smoother idle condition.

My '79 SD liked about 900 rpms, which I thought was too high. My '83 only wanted to idle smooth at about 650, which I disliked even more. My '82 was about 750, IIRC, as is my current 300d.

You are using a GOLD rack damper bolt, right? The original bolts were silver and they were just a hair too short to compensate, as the pumps aged. You need the updated gold bolt.

If you can't get it smoothed out via those adjustments, it's time for a compression test.

I agree that a bad motor mount may be causing part of what you feel inside the car. But if you feel like you're got a cammed V8 under the hood, when you come off the highway, there's way too much rocking happening for just a mount issue.