Professor wrote:
>
> There is a mechanism to kick the idle when the compressor load comes
> on. The idle should stay about constant. However, Brian may be right
> that your compressor may be binding. You need to loosen the compressor
> belt and rotate the compressor manually to check for excessive
> friction/binding.

Turning the compressor by hand might not tell you anything. If the
clutch doesn't engage when the engine isn't running, the pulley will
turn free even if the compressor is seizing.

I'd have the shop check out the idle control. Engines shake when they
are lugged below their normal idle speed, which sounds like the symptom
described.

--
Paul Hovnanian mailto:Paul@Hovnanian.com
------------------------------------------------------------------
Any sufficiently advanced technology is indistinguishable from a rigged
demo.