I checked all the vacuum lines and they were all connected. Nothing loose from what I could tell either. A few days after I first started this thread, the CEL came on and the RPM flutter has continued. I haven't had time to take it in to AutoZone to have the code read yet but this morning, the check engine light went off and the car seems to be behaving normally again. I haven't noticed the RPM flutter at all today.

On the other hand, my gas mileage took a serious dive since the CEL came on. I'll be lucky to get 300 miles out of a tank when I usually get 370-380 miles between fill-ups.

Wouldn't the engine be running a bit on the lean side if there was a vacuum leak somewhere in the intake track? Or is the ECU overcompensating for the increase in air volume by running rich?

In any case, I'm now thoroughly confused so I'm going to hook it up to an OBDII scanner and see what, if any, codes come up.