1996 SC1 hunts for idle in gear

I maintain a 1996 SC1 for a friend. She purchased this car a few months ago from a friend. This car has been very well maintained and seems to be a very nice car. It seems however that when it is in gear at idle it hunts for awhile. It fluctuates about one mark on the tach, and at the lower end there is a noticable harmonic vibration. I assume the vibration is inherent in the engine, but the idle shouldn't hunt. Possibly an idle air bleed valve? Injector cleaner? I normally work on other brands and am not familiar with Saturn. Hopefully you guys can help.