I'll add that I have an extra plug like you're describing as well. I'm not sure what it goes to, but I verified that all four injectors were plugged up, and I have one of those little dealies with the knob on top of the valve cover. My truck doesn't have AC though.

I just assumed it was something to do with the AC, so I just left it hanging there near the plenum. Truck runs fine. <img src="/forums/images/graemlins/confused.gif" alt="" />