Ok, thanks. Wasn't sure because after unplugging the IAC the car would start, but then die within 5 seconds. Had to give it some gas to get it to finally stay running long enough to adjust that screw. Even then it ran rough as crap the whole time I was adjusting that screw.
Even after screwing that threaded rod "out" as far as it would go the car is still only idling at 550.
Also I probably should have initially clarified that the car idles around 700-800 when in park, but only at 500 when in drive with foot on brake.
2005 F-250 Crew Cab Triton V10
1996 Mustang GT 4.6L
1995 Mercury Sable 3.8L