Vacuum Hose?
 

My 96 Yukon (5.7, 4wd) is idling rough. Have replaced the plugs, wires, cap, rotor, and belt. There is a spot near the throttle body that looks like there ought to be a vacuum hose, but nothing is there. I've attached two pictures, one closer up and one with a wider view. Look in the dead center of the picture at the blue plug. The piece I'm talking about is a black rubber tube with a 90 degree bend just to the left and below the blue plug. Is there anything missing here (besides my own knowledge of this thing!)?
Thanks in advance.
Craig

If its sucking air and you cant find out what runs to it, then plug it off. A vacum leak on those motors will make it run like crap especially at idle. So plug it until you find out what it runs off of.