Make sure you clean the connectors too. It may be possible to set the hard idle on the 4.0 (it's easy on the 5.0). Try this:

Run the throttle stop screw in several turns

Disconnect the idle bypass valve

start truck and adjust idle to desired setting with just the screw (make sure truck is warm and in close loop, thermostat will be open)

shut truck off and disconnect battery

reconnect idle bypass valve

after at least 10 minutes reconnect battery

start and drive the truck

What this will do is let the computer use the idle bypass for variances in idle and not rely on it to maintain the idle. Variances are compressor kicking on etc....

I have done this many times on a 5.0. It will work on any ford eec iv ro eec v that has a screw for a mechanical throttle adjustment.