I have dealt with this. I replaced every single seal in the throttle body about 2yrs ago. That screw controls an air bypass channel (bypassing the butterfly). If I recall, it wasn't supposed to be adjusted, it was factory set. I feel like mine may have had sealant on it too, but I completely took mine apart. You sure there isn't a screw hiding under there? It does adjust your idle but again it isn't supposed to be used for that because the IAC is supposed to control your idle. Anyway after I put mine back together, I got a loud hissing sound when I returned that screw to where I thought it was supposed to be. Too much air flow I thought, but it had to be there to get my idle right. My idle still wasn't right though, as I said, to get it to the spec RPM, the thing hissed so loud I could hear it in the cabin. I ended up taking it to dealer because there is a calibration procedure that requires a dealer tool which electronically forces the IAC to hold a certain position while that idle adjustment screw is set. Once it is set, it should never need adjusting. The dealer didn't know they even had this tool until I showed them a printout from the FSM. They found the device in their basement and used it. She's idled like brand new ever since. My theory is that since my rebuild increased my displacement ever so slightly, that it required this recalibration to make it Mitsu perfect again. Good luck. I think some higher end scan tools can support the IAC recalibration, but mine didn't.
