Vibration at idle?

["Reid, Les C." <Les.Reid@centrilift.com>]

My 89 200T 10v Automatic sometimes vibrates when in drive at idle.
The tac reads somewhere around 750rpm.
If I press the gas slightly to hold 800-850 rpm then the vibration goes
away.
I assume the car is just getting up in years and the rubber parts
(dampeners/mounts & such) are just getting hard & worn out.

Will replacing the rubber parts make and improvement?

Anything wrong with increasing the idle speed to 850 rpm?

Thanks

Les Reid