My 3 is having a bit of trouble idling fast enough. it drops many times to 750-600 rpm, and as a result develops way too much vibration in the cabin. What are the possible causes for this?

 

I'll check on my way home tonight, but 600-750 sounds about right.

 

Mine sits at just about 600-750 warm or cold.

 

yea that idle isn't out of spec. Could have a motor mount issue... or need plugs or something that would even out the idle a little. You can always shift into neutral when stopped which would raise the idle a little bit.