Hey guys..

So I'm working on the 300SD I drug home over the weekend. The car has been sitting since 2015. Its been ran a few times but not driven. The car was fueled on veggie oil for 40k prior to it being parked in 2015 with a misfire issue.

I found the misfire issue (air intrusion issue) and got it running relatively well but it has an odd issue.

As the engine warms up, the problem gets worse.

The engine idles a little high and if you touch the throttle at all, the engine just slowly climbs in rpm until it reaches the governor. Bump the STOP lever and it'll calm back down.

I'm linking a video to show what it's doing.

I'm sure it's something internal to the pump sticking that shouldn't be sticking... likely from sitting for years with SKUNK fuel in it. It's currently being ran from a fuel jug. I replaced all of the rubber fuel supply and main return lines and its ran now for ~30min or so on fresh diesel from the jug. I shut it down and put around 50/50 blend of atf and diesel in the container and ran it for another 20-30 minutes and i shut it down to sit overnight with the pump full of atf/diesel.

Tomorrow, I've got 4 cans of diesel purge showing up so planning on doing a purge thursday when I get time after work.

Any other ideas? Again, I've made no adjustment to the pump or anything... have no idea what has been done to it.

See video. Be sure to turn on sound.
https://imgur.com/ntjAT0g
https://imgur.com/ntjAT0g

Back the Rack Damper/Governor Idle pin out so it has no effect even after you re-adjust the idle with the proper idle screw. Not your idles speed is not supposed to hang on the Rack Damper/Governor Idle pin.

And see if that changes the issue. If it changes the issue for the better look up the proper method of adjusting the Rack Damper/Governor Idle pin.

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84 300D, 82 Volvo 244Gl Diesel

Will give that a shot tomorrow or Thursday.


I just printed out a fairly well written pump theory of operation and adjustment procedure of all the governors and such. I spoke to the original owner a little bit ago and he said the pump wasn't messed with. He installed this pump when the original bit the dust. Before the air leaks were fixed.. you had to hold the throttle open to get it to idle when cold. I'm banking on he cranked the idle up to compensate and then couldn't figure out the issue after the fact.

He could have used the wrong screw to increase the idle.

Just out of curiosity have you tried removing the linkage from the Throttle Arm on the Fuel Injection Pump and seeing if that cures the issue.

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84 300D, 82 Volvo 244Gl Diesel

No but I can physically watch the linkage return to the idle position as soon as I let go of it... but the engine rpm just gradually keeps climbing until it reaches the governor speed.


I can even force the linkage back as far as it will go and it wont slow the engine down until bumping the stop lever.


Its almost like the idle governor isnt doing anything... its either sticking or not adjusted properly.

It still looks like the linkage is catching. In my experience it tends to bind up on the top of the valve cover where the transmission shifting links are.

Check the cylindrical bushing that slides in that groove, sometimes it will wear enough that it catches in the groove.

If nothing else I'd disconnect the links labeled "B" and "A" on the first image in the thread below. This will isolate the pedal to the IP. If the problem doesn't persist then its definitely one of the other links.

Flow chart for transmission linkage 1985 300D

(Not sure why I couldn't post the image, it doesn't like it)

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Onus probandi incumbit ei qui dicit, non ei qui negat

I recondition w123/w126/w124/w140/r107/r129/ steering boxes!


1984 300D "Elsa" odo reset 6/2011 147k
1983 300TD "Mitzi" ~268k OM603 powered
1995 E300 "Adelheid" 262k [Sold]

I'll definitely check it out. The only oddity about it if it were linkage related is that after bumping the stop lever, it will fall back to a high idle and not just continue to rev back up which I would think would be the case if the linkage was stuck or sticking.

If idle is too high speed will increase,set idle slower retest

I can't say I have read this officially but quite a few members have said that the governor only has control at idle and the very high rpms. In between that it is your foot controlling it.

I have read of the same symptom you are having and they said it was because of the Governor Idle Pin being turned in too far. Also the Governor Idle Pin pushes on a different lever inside of the Governor. If there was other reasons for the same symptoms I don't remember them as that discussion was way back around 2010.

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84 300D, 82 Volvo 244Gl Diesel

The one I used to have did this and changing the injection pump fixed it. One of the idle adjustments was broken but I had driven it for years before it started doing that.

If the normal idle adjustment breaks off there is a fix for that. I cannot post a pic as I am on a Computer that dose no have my pictures.

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84 300D, 82 Volvo 244Gl Diesel

Any possibility that the cruise control linkage might be causing problems? Just a SWAG.

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

OK... so I did the purge. Didn't fix it.

I unhooked the linkage and the arm on the pump snapped forward. When it starts, it revs right up. If I push the arm back to line up with the linkage, it idles down. The linkage is holding it back at idle.

Something on the pump is holding the throttle open nearly 1/4 or more with the linkage unhooked.

The idle screw itself isn't touching the arm but something spring loaded coming from the bottom of the screw is pushing the throttle open a good bit. If I push the stop lever back to an idle position, I can see something retract into the bottom of the idle screw.

I'm guessing idle screw is in too far?

The Idle screw has a spring loaded plunger.

In normal operation the Throttle lever is stopped by the Spring Loaded Plunger and where the Throttle Lever Stops sets your idle speed.

When you use the manual shutoff lever it pushes on the Throttle Arm and collapses the Spring Loaded Plunger up into the Idle Adjustment Screw.

Back off the Rack Damper/Governor Idle Pin and see if the Throttle returns to the normal position.

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84 300D, 82 Volvo 244Gl Diesel

I'll give that a try here in a bit.