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1984 300D
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11 Posts
Discussion Starter #1
My recently aquired 1984 300D with 175K has somewhat of an idle shake. It also seems to run a little rough in the lower rpm ranges but this can only be noticed when running the engine up from idle in park. Car seems to be very well maintained according to records and has had valves adjusted within the last 10K. Also, new rack damper bolt installed. While I do not know the condition of the two engine shocks since I have not had them off, the motor mounts "appear" to be pretty solid and not broken. I do not know if they have been replaced but I will look in records.

I have done the following: New Rack damper bolt was screwed in almost all the way. I backed it out and the engine responded well and smoothed out some. I do have the air cleaner mount issue but that is minimal and not causing the shake felt inside the car at idle mostly after warmup.

I think my idle speed may be a little high, but I also think the tach in dash may not be completely reliable. I estimate 8-900 rpm, but there is no bad "thud" when placing in gear. When I push on the injector pump stop lever about 1/4 inch which pulls the rod up, engine slows down a little and actually seems to run even smoother.

Car otherwise starts and runs well gets approx 29mpg highway and seems to have great power. I have the MB manual and have had experience with diesels but not MB diesels. After reading some of the related posts, I am hesitant to adjust the ALDA at this time.

Could this shake be related to the position of the IP throttle rod at idle?

Perhaps a dirty injector? (before removing is there an effective additive that is worth trying?) (BG 44K works good for gas engines to a point. Is there something as effective for diesels?) additives are not a favorite thing of mine but perhaps worth trying in this case?

I would like to follow a procedure here that makes sense.

Thanks very much, Steve
 

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1991 300zx 2+2 @ 129k Miles.
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194 Posts
Idle shakes are similar to what I had when I first got mine early this year. Take a look at the motor mounts.
 

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1984 300D
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5,070 Posts
What I had to do to get rid of the my when Engine hot vibration/shaking:

Raise the Idle speed within the normal range (this helped some; it was around 700rpm). I raised it to about 750 rpms.

I bought a new Rack Damper Bolt but it did not help much (like changing the Air Filter Bolts it will not cure vibration caused by other things; will come back to that later)

Rebuilt my Injectors with $16 each brand X Spray Nozzles (This took away most of the shaking)

Doing a Valve Adjustment (took away some more shaking). If you can adjust the Valves yourself do that first except for the new Valve Cover gasket is free.

Changed Motor and Transmission mounts (took away some more vibration)

Found that I had a small air leak that showed up when the Engine was hot due to hard fuel inlet lines that did not seal even with the clamps tight.

Finally was able to use the Rack Damper Bolt to tune out a little more shake. (that bolt was made to reduce the shake on a new engine; not to compensate for a bunch of worn and out of spec parts
 

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2001 Volvo V40
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2,954 Posts
Although I have a different engine, adjusting the IP timing back to specs (from 24 degrees to 26 degrees) finally removed my idle shake.

There are laser pointers which can measure rpm if you put a small piece of white reflective sticker tape on the crankshaft, that way you can check the idle speed.
 

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1984 300D
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11 Posts
Discussion Starter #5
Thanks very much to everyone for the advice on idle shake. It seems that checking everything starting with the simple stuff is the way to go. Engine mounts are fairly inexpensive if they have not been replaced. IP timing it would seem pretty critical to this as well as valve adjustment. Will proceed slowly and keep you posted.

Best Regards, Steve
 
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