For some reason, my W210 has recently started idling seemingly a bit too low while in "D". It idles around 600 RPMs and it creates some vibration. When I put it into "P" or "N" it idles a bit higher and smooths out.

The vibration is highly irritating at stoplights. What is it supposed to idle at AND if I can adjust the idle myself, how do I do it?

Thanks, -DL