I oughta warn you I am still learning about Fords. But since nobody else has chimed in yet

IAC is a valve that is in a path that goes around the throttle body (to bypass it.) The throttle is closed at idle and the IAC adjusts air flow. Sometimes they stick in a place that lets too much or too little air in for idle. Sometimes they stick in a place that idles okay normally and then it can't move to compensate for a change.

Air leaks that matter are anywhere between the air flow meter and the cylinder intake ports. There are a bunch of things that come off the intake plenum to provide vacuum to other devices.

You can disconnect these items and plug the ports, generally without trouble:
Brake booster
4WD controls
Air conditioning controls (flap motors)

These items may cause fault codes to be set:
EGR control valve
EVAP control line
EVAP purge line

Unplugging the vacuum to the fuel pressure regulator will cause high fuel pressure. This will richen it up quite a bit.

A stuck-open pcv valve is a giant air leak. They are supposed to be free flowing at low pressure and restrict flow at high pressure.

You mentioned an oxygen sensor code in your first post. The front o2 sensors - before cats - regulate fuel mixture. The lifetime of an o2 sensor is about 100k miles. Then it starts to report to the lean side, causing the engine to actually run rich. However, they go bad in a way that gets worse over time. The exhaust usually plugs up (running rich clogs up the cat) before people notice idle issues. If an o2 sensor wire was broken, it would not be possible to warm up the truck without getting check engine light and fault codes about it.