Have you adjusted the throttle stop on the TB?
Base idle screw is the screw that the throttle butterfly rests on. Its underneath the throttle body.Where exactly is this base idle screw? Is it the flat head screw by the IAC? I replaced the IAC by the way with zero success. If this does not fix the issues, I am just going to put my old stuff back on. By the way, it idles at 1500 but once I took it for a drive, it got stuck on 2500. Once I unplugged the IAC the idle was perfect.
SR Performance Mustang 75mm Throttle Body 41114 (94-95 5.0L Mustang) - Free Shipping (americanmuscle.com)