ROUGH, LOUD idle 1983 300D

Hi,
Went on a road trip last weekend, and after driving down a steep canyon, my car became LOUD! Really only at idle speeds, when I speed up it's much better. But the whole car now *shakes and is incredibly
*loud. Perhaps a coincidence this happened after I put stress on the car? Or not?
Could this be the fuel filter/pre-filter? I changed them about 9 mo ago, but it was VERY clogged when I did it then, so wouldnt be suprised if it was time
More likely the valves? If so, any suggestions on how to check these?
Motor mounts? How do I check this?
Thanks, Kate
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There's nothing wrong with the fuel filters if it pulled UP the hill.
The valves are OK if the motor starts easily when cold.
It's loud and horrible at idle when hot for a reason that's either an easy fix or a more difficult one.
The easy one first. Five cylinder motors are inherently unbalanced and shake some at idle. The problem is that its small scale shaking is an oscillation that affects the fuel rack inside the injection pump which controls the engine's speed. So then, the idle speed rapidly increases and decreases and the whole car shakes in sympathy. This occurs mostly after freeway driving that has really heated the motor.
There's a fix that's easy to do. Look at the aft end of the injection pump - near the pipes to the oil cooler. On the pump is a bolt with a lock nut. That's the "rack damper pin or bolt" a spring loaded pin that ought to just bear onto the fuel rack to prevent it from oscillating. The adjustment is to loosen the lock nut and slightly tighten the bolt and snug up the lock nut. Too much IN will cause the motor to stall so do this in stages of say 1/4 turn - try it - 1/4 turn if needed etc. M-B sells a 2nd version of the bolt with a stiffer spring for about $25. First try adjusting to original one. I've adjusted this an seen the motor go from heavy shaking to quite smooth with a very small turn of this bolt. Given your description and lack of prior problem I suspect this is the motor's issue.
If the rack damper adjustment / replacement fails to cure it then you have to consider the motor mounts - don't mix them there's a left and a right to them.
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First thing I'd do would be to run two cans of Diesel Purge through it.
--
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Richard Sexton | Mercedes stuff: http://mbz.org
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