Okay, so for a while now, the SDL has had a stop lever on the IP that has a tendency to move up and down sort of like it's floating in wavy water - while the engine is running and idling. When you rev the engine up some (not to a high RPM but just basic acceleration to 2K or 3K) and then drop your foot off the accelerator in one swift motion (don't gently decelerate, but just let the pedal fly back to idle like you were going for the brakes) then the lever takes a nose-dive as the RPMs near idle and almost chokes the car. It then surges back into position before the car officially dies. It doesn't *really* reduce the RPM down to a level that should kill the engine, it just goes from the normal idle down 50 or 100. It produces a noticeable effect when this happens; I can hear and feel the speed drop momentarily.

I did some searches but it's hard since everybody has a different word for "bobbing up and down". I've run across the following suggestions so far.

1. Vacuum valve in the ignition switch is failing, allowing vacuum to leak.
2. Governor springs and weights in the IP are worn out or badly adjusted.
3. Somebody said that replacing their delivery valves cured the problem.

Obviously I could check for the first theory there (I haven't yet, *slap on the wrist for posting without having performed a known test first*) - I'll go out and try that next time I have a chance, assuming it's doing it today. That test would be to just unplug the vac line to the IP (It'll probably break) and see if the bobbing stops.

IF we assume, for the sake of troubleshooting, that it's not vacuum getting to the IP when it should not be, are those other two theories likely explanations? What else could it be? What should my diagnostic process begin with?

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

How much force is moving the lever? Can you hold it steady with a finger?

AFAIK the shutoff lever connects to the governor and such through a slot. The IP innards can do what they will and it won't affect the shutoff lever. Only the vacuum actuator can move the lever. But anything can happen if the innards are bent or jammed.

Sixto
87 300D

I saw my friend's 603 stop lever and it was stable, while mine moved as yours did. I replaced the shutoff valve (it was plastic and cracked). The lever was now stable at idle. I also noticed the car was a bit more peppy. Check to see the the shutoff valve pin is in the yoke, mine rode above the yoke.

My '87 300D Turbo (W124, OM603) has done a little bit of that; I originally thought it was causing my lack-of-performance problem. However, when that problem went away on its own, I didn't look further at the stop valve. Perhaps it is worth revisiting.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Ive done lots of reading on this as mine has "SURGED" since i own it and the best answer Ive seen is that un-tuned injectors can cause this. I have a nailing injector and am hoping when i take the plunge to TUNE ER UP with injectors and glow plugs, that it will settle down. i did a recent ATF injector cleanse through the tank and its seems to surge less right now, confirming my suspicion

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[B]AlanT
BELEN NM


93 dodge cummins truck~old reliable
01 Volvo AWD XC70 Turbo Wagon
74 450 SE on the way out!
Recent: 1972 Toronado 56k on the clock!

IF it plugs in, lights up, makes noise,
I'M ON IT!