Mine had the same problem. The idle was set around 750 and when the compressor kicked on it would drag the idle down enough to cause some wicked shakes. I raised the idle to about 800, I'd say, and now it feels the same whether the compressor is on or off. You can't even really tell when the compressor kicks on.

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Seth

1984 300D 225K
1985 300D Donor body
1985 300D Turbo 165K. Totaled. Donor Engine. It runs!!!
1980 300SD 311K My New Baby.
1979 BMW 633csi 62K+++? Dead odo