I am trying to narrow the choices of where to look for some really odd vibrations coming from my 84 300D and I thought I would enlist your collective help.

At idle (750 +/-) the engine is a bit shaky - BUT when the A/C compressor engages the car really starts to do a jig. It feels like the car is gyrating from under the front seats and she moves a bit up and down in a circular motion. Smoothes out to it regular idle shake when the A/C compressor disengages. Ideas?????

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paul300td

I have an 83 300D with the exact same problem:
The dreaded rough idle

You can see what I've had done to the car (all suggested possible fixes from the research I've done) with some results, especially the valve adjustment, but nothing has fixed the problem thusfar.

Good luck.

Replace both front motor mounts.

Have a great day,

Motor Mounts are Newish
Valves Adjusted
New A/C compressor
Belts

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paul300td

What is "Newish?" Have they been changed since the problem started and did the problem go away after replacing them? How long ago were they replaced?

Vibrations are among the most if not THE most difficult problems to troubleshoot via the internet.

Good luck,

They look lioke they are fairly new - perhaps the PO replaced them. I have a pair here I will put on to see if that does the trick.

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paul300td