UPDATE:
OK. I just remembered that when the Check Engine Light first came on (and would shut off shortly there after), I had stopped at a different Advance Auto and had them run the codes. I found a printout in my glove compartment.
These are the codes from a couple of months ago.
P1151 - HO2S Bank 2 Sensor 1 - Insuff. Switching - Lean Mean
P1519 - Intake Manifold Runner Stuck Closed
Sorry about adding this to the mix, but I didn't think that I still had the code printout until I dug around more for it.
I am going to pop the hood next and listen for a hissing sound...
