Car revs itself up?

[V10SpeedLuvr]

I was out cruising in my 96' RT/10 tonight and noticed while I was stopped with the car in neutral (either foot on brake or not on brake), the tach was jumping b/t 500 and 1000RPM. I dont recall it doing this before. I was in a bunch of stop and go traffic. All the gauges were fine and no idiot lights ever flashed or came on. Besides this erratic idling, the car drove fine. Is this normal? If not, what could some of the culprits be?

 

[Ulysses]

IACM, Throttle cable sync, vacuum leak.

 

[IEATVETS]

Sounds like the beginning of the dreaded "idle hang" which most of us know a lot(or a little) about.