This is a problem from an inherently unbalanced (5 cylinder) motor, a
too heavy air cleaner can and a poorly designed support bracket.

In my 26 year ownership the support bracket under the air filter can has
broken three times - always the rear leg. The newest one has a
reinforcement welded to that leg to help it take the motor's side to
side oscillation. I also screwed onto the air cleaner can a metal
(plumber's) strap enclosed by a piece of heater hose as a bumper between
the air cleaner can and the engine's valve cover - again to reduce the
air cleaner's oscillation.

Notice that I didn't even mention the three rubber mounts for the air
cleaner car - their failure is assumed after about 10K miles.

1. Try to lift the air cleaner from its mounts - the can will lift if
one of the rubber mounts is broken. These are about $10 each at the
local stealer but cheaper on line.

2. When the motor at idle sounds like a semi automatic, the support
bracket has broken and needs to be replaced. Suggest a steel semicircle
arc be welded to the new bracket to stiffen its rear leg - but not so
large that it won't fit.

3. The rack damper pin is adjusted correctly if the motor doesn't shake
heavily (1/2" or greater oscillation) at hot idle. The shaking is awful
and suddenly stops with a slight turn of the bolt - day vs. night. So,
unless the whole car acts like a jumping bean at hot idle, leave it
alone for its either OK, or not.

If I have further problems with this lousy design I'm going to mount the
air cleaner can on the fender and pipe the air to the turbo.

Looking for the root cause? Check out your motor mounts. The shaking will be
bad if the mounts are worn out. Not too expensive to buy, but a little bit
of a pain to change. At least the first time it was. I have a '84 300D.
Changed the mounts 2 years ago. Been smooth since then. I, too, had a
problem with the air filter mounts. But it hasn't broken since I changed the
mounts.

Bill

Varnish inside the injection pump. Run two cans of octalnitrate
throgh it. "Lubro Moly Diesel Purge" is what I like right now
and I'm 99% certain if you run two cans thourgh it it'll smooth
right out. You don't do this every now and then I take it? You
need to to to clean the gum, varnish and other deporist than tens of
thousands of gallos of gasoline leave on the inside of fuel handling
machinery.

Don't go for any addiaitve in a tank stuff, you haveto run the engine
on this crap for 15 minutes directly, but it's easy and bloody magic
in what it does. Anything with octal nitrate should work, but most stuff
i've sen is stupid expensive and the German Lubro Moly stuff seems
to be the cheapest source at $4 a can or something like that.