The Motor will surge in RPM at idle when in park or drive. It is more noticeable when the car is first started, but it continues after it is at operating temperature.

The timing chain was replaced 10,000 miles ago. The car has approximately 80,000 miles on the motor with no other problems.

I would suspect a problem with the idle control system. The system resets itself if it can't achieve desired idle speed. Look for vacuum leaks and be sure the throttle is fully closing. If there are reasons for a high idle the valve will be commanded closed. It may actually control the speed at times, but at others it won't and when the system resets the speed surges.