2001 Buick issues with starting and staying started

Ok we checked the IAC Valve and cleaned it. It was completely balck and on of the screws were missing when I took it off. Would one screw missing cause this part not to work properly?

Car is fixed!!! My husband was looking at the IAC Valve to put in an other screw this morning and found a hose that was sliced down the side and an other valve of some sort that had gas leaking out of it. Come to find out that only air was suposed to go thru there. We got that changed, an other $60 part. But now it starts at the slightest turn of the key and does not suppter or stall out on me. Thank you for all of your help, it is greatly appriciated.

The car is fixed, when my husband was putting in a screw that was missing; he and his brother in law found a spliced hose and a valve that was only suposed to allow air to go in or out threre was gas leaking. Replaced that and now it is running like a dream. Thank you all for your help. It is greatly appricated.