How hard is upgrading the idle adjustment bolt? - PeachParts Mercedes-Benz Forum

bigfredb · #1 11-11-2008, 03:23 PM

I have an 83 300SD

I'm having a problem with a rough idle (especially in Drive while waiting at a stoplight).

I took a look at the idle adjustment bolt and it is the old style and adjusted all the way.

How hard is it to upgrade to the new style idle adjustment bolt?
What does it entail?

Brian Carlton · #2 11-11-2008, 03:27 PM

Loosen locknut.

Unthread adjustment bolt.

Install new adjustment bolt.

Tighten locknut.

Some experimentation of the position of the bolt is required to effect a smooth idle without affecting the cold start capability.

zeke · #3 11-11-2008, 03:52 PM

^^^
x2 - Just did it in my 240D over the summer - I lost my original one - it fell out somewhere, somehow.

meltedpanda · #4 11-11-2008, 05:18 PM

do this adjustment when the engine is hot - turn till it bucks and moans then back to smooth idle, lock it in. Once again - do it hot
once again
It should just barely make contact and damp the shake (when
EVERYTHING is running correctly and the engine is WELL
warmed up) then loosen it 'til it shakes - then tighten 'til
it just stops shaking. Then tighten it down.

bgkast · #5 11-11-2008, 06:17 PM

Are we talking about the rack damper pin or the actual idle stop bolt here?

meltedpanda · #6 11-11-2008, 08:14 PM

well I am talking about the rack damper bolt, but now that you ask, ????

bigfredb · #7 11-12-2008, 03:30 PM

I didn't realize there was a difference between the Rack Damper bolt and the idle stop bolt.

The bolt I am referring to is the bolt coming horizontally out of the aft (back) portion of the IP. It has a nut on it to hold the adjustment.

Is there enough room to easily R&R the bolt without removing anything else?

bgkast · #8 11-12-2008, 03:41 PM

That is the rack damper bolt, and yes, it can be removed with out the need to remove other parts.

meltedpanda · #9 11-12-2008, 08:00 PM

why not try to adjust the one you have, the purpose of the bolt is to dampen the rack movement, if your is in all the way , you may have other issues. I assume your engine shock and engine mounts have been checked?
These can be the cause of many a vibrations!

Diesel911 · #10 11-13-2008, 12:33 AM

After reading the comments on this Forum an my own experience I think that the Rack Damper Screw/Bolt was ment to reduce the shake on an engine with no other issues going on (as in new car). So, depending on the condition of your Engine and what supports the engine replacing it may or may not help.

I bought a newer (Gold) Rack Damper Screw and found it did not help much until after I took care of the Valve Adjustment, rebuilt the Injectors and replaced Rubber Engine/Transmission mounts and 1 Engine Shock.

After the above was in order I was able to remove a little more shake with the Rack Damper Screw. (Still have not re-timed my IP maybe doing that will get rid of some more shake).

When I compared my old Damper Screw to the new one I found that the tip if the plunger on the old one was worn and that the spring on the newer one was almost 2X as strong. So it may be that updating to the newer style could be helpful if the older one is worn and the spring is weak.

bigfredb · #11 11-13-2008, 05:11 PM

The Rack Damper bolt is adjusted all of the way in at this time. It is the old bolt so I was looking at upgrading to the new bolt (its longer, i guess). I can almost bet that the old one is worn.

The shakes are only really apparent at low idle after the engine has warmed up some (mainly when I am stopped at a signal). The shakes happen most of the time, but not all of the time (even on the same drive). If I give the engine just a touch of fuel with the pedal, the shakes minimize considerably.

The Engine mounts and engine shock mounts are new. (w/i the last 6 months)

I am planning to change out the fuel filter, inline fuel filter, and hand primer pump tomorrow to see if it has any effect (its been 5000 miles since i changed them).

Any other observations would be helpful and appreciated.

Chad300tdt · #12 11-13-2008, 05:35 PM

Make sure you've adjusted your valves first and set your idle speed screw so you're idling at 750 and not lower.

Then you can adjust the rack bolt if needed. Mine was turned all the way in and the engine shook at idle. I removed the bolt completely to check the pin. It was still very firm, so I reused the silver bolt and screwed it in until the idle smoothed out. I could do a 1/4 turn on the bolt in either direction and the idle became shaky again, so I locked it down and it's been fine ever since.

My point is, just because the bolt is all the way in, doesn't mean it's beat. Test it first. It was a PITA to remove and replace the bolt due to tight quarters. I had to use two finger tips and start the threads blindly while burning my hand on the operating temp parts.

meltedpanda · #13 11-13-2008, 07:05 PM

adjust the one you have as i have indicated and make sure the engine is HOT!
Just be careful. The new bolt is not longer, just a firmer spring. If you have replaced shock and mounts ,that is your next step. I read your post , surely you are not repalcing the primer pump after 5K , mine had 175K on it before I replaced it

Diesel911 · #14 11-14-2008, 09:59 PM

Quote:

Originally Posted by Chad300tdt

Make sure you've adjusted your valves first and set your idle speed screw so you're idling at 750 and not lower.

Then you can adjust the rack bolt if needed. Mine was turned all the way in and the engine shook at idle. I removed the bolt completely to check the pin. It was still very firm, so I reused the silver bolt and screwed it in until the idle smoothed out. I could do a 1/4 turn on the bolt in either direction and the idle became shaky again, so I locked it down and it's been fine ever since.

My point is, just because the bolt is all the way in, doesn't mean it's beat. Test it first. It was a PITA to remove and replace the bolt due to tight quarters. I had to use two finger tips and start the threads blindly while burning my hand on the operating temp parts.

The new Gold Rack Damper bolt also has the same limited "sweet spot" as mentioned above.

ashedd · #15 03-08-2009, 06:36 PM

I have looked and looked. I have a good idea how to adjust this bolt BUT I have yet to find a picture, as usual. I need to know where this bolt is located on the IP. I am loosing daylight here. 83' 300SD shakes bad when hot.

Thanks

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