Motor Mounts will NOT make the Tach. move around!!!!!! These cars are VERY lean at idle, a spark plug will mis-fire and cause a SLIGHT SHAKE in park. When put into Drive, there is enough load on the motor to slow the idle enough to smooth it out!!!!!
I've dealt with this to varying degrees the entire time I've had this car (almost 2 years) and after going through the usual suspects (mounts, plugs/wires, maf, etc.) I believe its the injectors (gas varnishing/gumming them up due to not being driven enough), since the only thing thats made a noticeable difference are fuel additives - specifically Lubro-moly Jectron (Chevron & Redline made no difference)
I've gotten it down to the point where its barely noticeable, so I've learned to live with it; but for a while I was considering ultrasonic cleaning - watch this for an example
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