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.