John, the whole ignition system is new installed by myself. I will try BG44k.

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11 S550
09 C300
91 560SEL
90 300CE
84 380SE
83 240D

The BG44k will do wonders, I usually don't believe in "snake oil" products, but it really works if used properly.

The local MB dealer stocks it for the service department if that tells you anything.

Well, I have a 1985 380SE and even before my car developed the engine "miss at idle when in park and when first shifting into 3rd and 4th" problem I would notice an occasional side to side movement when I was setting at a stop light or something. Sometimes it does not do it at all. Heck, I may need some of that BG44k stuff.

I am still working on mine.... I have heard my problem could be a vacuum leak, fuel pump relay, spark plug wires, etc. So, my next purchase is a FPR, or at least try to test my car to see if that could be the problem. I also have an occasional stalling of the engine, but only when outside temperatures are above 70°, but spring and summer are coming, so I need to fix whatever this is.

John said, "assuming that the valve guides are not worn" - thats probably my luck and whats wrong with mine, as I have 269K and people wonder why I do not want to spend $$$ on this car.

I almost bought a 84' 300SD, with 335K. It had a horrible engine shake.... it would violently shake at idle, but with even the slightest acceleration, it would smooth out completely. I had no idea what what was wrong with it, as I came here and I was told it could be bad news (bad compression), vacuum leaks, bad injectors, or as simple as a bad motor mount..... more of that "wild goose chase" info.

SO- I bought a 1990 Lexus LS400, so I can relate to your statement about it being smooth as silk. My car had 245K when I sold it and the engine and transmission were still as smooth silk.... flawless. I would have to look at the tachometer to see if the engine was still running when I was at stop lamps. I sold it because my A/C evaporator went out, as was my radio (it would only work when outside temperatures were above 90° for some reason). I sold it to my grandfathers pharmacist, who crashed it a few weeks later.

I currently have a 2000 Toyota Tundra pickup, with the 4.7L V8, which is supposed to be based on the Lexus V8 design (which is actually the same engine used in the Lexus LX470 SUV). It too is as smooth as silk... you cannot even hear it run at idle and I have to again, look at the tach to see if its still running.

Nope, a well tuned, and as you have already replaced the engine mounts - rule that out, 126 does not shake, you could balance a coin on the dash if they are running right.

Mine is quiet and still at idle, you have to check the tach to see it is on.

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1988 W126 420 SE

beware of fundamentalists!

My 85 380SE with approx. 131,000 miles idles smooth as silk. Can't even tell the engine is running. I know the PO replaced all the engine and tranny mounts and shocks. Even if yours are new it is possible you have one or more defective parts. Even new parts are occasionally defective.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

I have both of these cars and the same experience as the Thread writer; the 89 420 has a slight roughness in the idle, not a shaking or anything -- but runs very well otherwise. (perhaps I need to run a can of the super cleaner through it? My 300CE idles smoothly.... Ben Carter

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Ben Harrison Carter
1999 Mercedes ML320 87K
1992 Mercedes 300CE 89K
1995 Corvette 29K -- Sold Dec 09
1989 Mercedes 420SEL 99K -- (Sold 4/08)
1968 Mercedes 230S (106K) (Sold 9/06))
1976 Mercedes 450SEL 130K (Just sold - 06)
1961 Mercedes 220Sb (sold years ago)

Mine (when I had it running) ran perfect.

New plugs, dist., wires, air filter, cam oilers, Resoldered Idle control unit and OVP.


now, if the fuel lines didnt rust out...

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-1983 VW Rabbit LS Diesel (5speed, VNT/Giles build)