Need some advice on how to adjust the idle speed on my new 300SDL. It seems that it shakes really good at idle - but especially when cold - I mean it will rattle the hood. When I bring up the idle speed gently with my foot the resonance and the resulting shaking goes away. When I drive, it's smooth as silk, but not so much at idle. Could this problem be caused by bad motor mount(s)?!

So how can I adjust the idle on this car and what should the proper idle be for this car?! I think it's currently hovering around 700-800rpm. It smooths out at about 850-900. Would this proper or too high?!

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1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K