I can see it happening because the shaky idle is a "comes and goes" thing. It often appears that the engine gets in a "positive feedback loop", aka a microphone too close to a speaker. The feedback might be from the shaking causing the IP to modulate fuel, which amplifies the shaking, at certain rpm's that match the "natural frequency" of the engine & mounts system. Being a "nonlinear effect", it sometimes takes a certain external excitement to get it started, and any little thing like a shaky air cleaner might be enough to push it over the threshold. Think of the "butterfly effect" in world weather. Sometimes a computer model even needs a little starting bump to get it to show oscillations.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Diagnosis of problems should always follow a linear pattern to avoid chasing your tail .

Most of the Vehicles I work on have been through the mill so they tend to have really obscure problems , often DPO & DPM bodges .

Fiddling with the rack damper bolt before you personally have cold adjusted the valves , as a waste of time and effort .

As a Journeyman Mechanic I always like to hear others ideas so threads that meander around are usually very instructive although not always to the original question .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Pure Vivid Imagination.

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

The rubber mount that I replaced over the weekend has already broken, so yeah, it was just a coincidence that my idle smoothed out at the same time.

If my idle gets rough again, maybe I'll do the same repair as kind of a rain dance ritual thing before I start adjusting valves and changing filters.

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'81 300SD

Me too. That's a new one on me.

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'06 E320 CDI
'17 Corvette Stingray Vert