I'm thinking IAC as well. What threw me was the POP it made. Backfire? I don't know where it came from as my back was turned when it happened.. I wasn't able to get back to the truck tonite, but I have a spare IAC that I can try tomorrow.
I checked all the vacuum lines and capped ports and didn't find anything. I did the plenum upgrade shortly after I bought the truck, hopefully that didn't go bad again.
