[ischmitz]

The first check is to make sure when the throttle is all the way closed the micro-switch on the throttle body is closing. This signals the computer that it needs to stabilize idle.

In your case if the fluctuations are that large it could be a vacuum leak somewhere on the intake. Did this set in gradually and got worse over time (points to a leaky deteriorating hose) or from one day to the next. (hose snapped off, switch doesn't close, defect in DME or ICV)?

Mileage (only 60k) isn't really the driving factor here. It is the age of components such as the rubber hoses that harden with time and develop cracks. They don't like the modern fuels with ethanol either and that sometimes compounds the issues.

Cheers,
Ingo