Here is a link to the tips and maintenance sub-forum with a picture pointing out the part in question (the picture is of a 3800, but the 3100 is similar).
http://www.automotiveforums.com/vbul...ad.php?t=74637
Unplug the harness, remove the two screws and remove it from the throttle body. here is a link to AC delco's website picture of the IAC.
http://198.208.187.182/internet/View...umber=17112350
The cone shaped tip (being held in place by a wire bail that won't be on yours, it's for shipping only and is discarded) is the piece that you need to clean, it gets carboned up. Be careful not to move the plunger in and out while cleaning as you can screw up it's calibration/adjustment.