It's the PCM's job to adjust the idle speed. When you mess with the throttle stop screw, you're messing with the amount of air that's going to be allowed around the throttle blade, which can lead to the PCM not being able to control idle speed at all, especially on warm days.
On older EEC-IV PCMs (say, before 1992 for our trucks), it's important to have the TP voltage in the range of about 0.8 to 0.95V, as many of those programs used 1.0V as a 'threshold' for off-idle, i.e. the driver wants to go! The same is true for most Fox-body Mustangs (I own a few of those too :toothless ). On the later Broncos, the throttle-closed TP voltage is of less consequence; it will automagically 'remember and update' the minimum TP voltage observed, which is a much more intelligent way of going about ascertaining throttle-closed position.
It's also important to remember that for idle speed to be correct, all of the other systems that can affect it must be functioning near-perfect. PCV, the vacuum controls (TAB, TAD, FPR, EVR), brake booster, MAP, CANP, etc. and all of the intake manifold gaskets and fittings MUST not leak or allow too much/not enough air to enter the manifold. It's sometimes a balancing act on crack, because the engine has virtually ZERO load on it at idle. So any additional air WILL increase idle speed in a seemingly disproportionate amount. IIRC, Ford targets the IAC to have a duty cycle of around 40% when the engine is new and is at SAE-rated standard temperature, pressure, and humidity.
If the vehicle was running fine before the TP went to shit, it should be just fine replacing the TP sensor with no other adjustment.
