Idle Governor and Rack Damper bolt - same thing? - PeachParts Mercedes-Benz Forum

D_Ryan · #1 11-17-2008, 08:44 AM

All;

Been reading through the threads, and see references to the Rack Damper Bolt and adjustment as a means to smooth out idle. I also see a few posts addressing a idle governor; are these the same assembly, under different terms?

Now that the temperatures are dropping in the "Old Dominion" (Virginia), my 1985 300TD is wanting to idle at around 500 rpm immediately after starting. Lightly depressing the pedal to get the revs up to ~750, and then driving off keeping the revs under 2K. A short while later it will idle reliably at 750 with no encouragement.

It used to be that I could watch the idle slowly rise as the engine warmed, and then the 'governor' (I assume) would pull it back down. Now that is not happening... (or in the course of driving the car it warms up to a point where the governor has no role).

Valves were adjusted approx. 5 - 7K ago, so I don't believe that is the problem.

Thanks as always,
Dave

Chad300tdt · #2 11-17-2008, 09:09 AM

Governor Idler Adjustment Pin and Rack Damper Bolt are the same thing. Signs of a bad or improperly adjusted bolt are rough warm idle, hard cold starts and RPM hunting.

Adjusting the rack damper bolt

You can adjust the Idle Speed Screw to raise your idle to 750.

D_Ryan · #3 11-17-2008, 09:38 AM

Chad, Thanks for the confirmation.

Sounds like more troubleshooting is in order... I don't have an issue with rough idle when warm, right at ~750 as it should be and smooth. The problem is that the car does not want to idle at ~750 when cold, rather it is down around 500 rpm (tach indication).

There is no indication that the governor is trying to pick up the revs as the motor warms either... and I can't really detect the rpm's trying to hunt (how much of a swing are we talking about?)

May be that the last valve adjustment wasn't all it should have/could have been...

r/
Dave

JimmyL · #4 11-17-2008, 09:42 AM

My '85 wagon has done the same thing for about 3 years. Just doesn't idle high enough when cold. Idles fine when warm, rpm wise, but could be smoother. I replaced old style rack bolt with newer style and it didn't make a difference. Mine never has that "magic spot" that noticeable smooths out the idle.....

Chad300tdt · #5 11-17-2008, 09:46 AM

Have you guys tested your glow plugs? My CD has been having a rough cold idle that smooths out as soon as the engine starts to warm up. It's only been an issue since the colder weather arrived. I figured I have a bad plug or two. I just have to get around to testing them.

EDIT: It starts fine, just a low RPM, rough cold idle.

JimmyL · #6 11-17-2008, 09:51 AM

Yep, tested glow plugs numerous times via the resistance readings. I guess I might need to pull them out and shoot 12vdc to them just to be sure........

Been contemplating that. Been putting that off.......

Chad300tdt · #7 11-17-2008, 09:54 AM

If the plugs test OK, I've read that some guys are having success with an afterglow upgrade. It's an expensive relay, but I heard you can get the same results by disconnecting the purple wire so you continue to glow for a full cycle even after the car is started. It's supposed to help with rough cold idle.