Welcome to the forum
Automatic or manual transmission?
EDIT: I see in the video an automatic shifter
On all engines RPM is control by air flow not gasoline flow, if you add more gas engine floods, less gas engine pings/knocks, but RPMs remain the same.
The IAC(idle air control) Valve is used to by-pass the throttle plate, IAC valve passes air coming thru MAF sensor not from outside the intake, because all air coming into the engine needs to be monitored with a MAF(mass air flow) system.
The whistling sound comment certainly reads like an air leak.
(side note, on the IAC Valve is a black cap that allows pressure to escape so valve can move in and out, if valve seal is not sealing well then you can get a whistling noise from under that cap, new or not, cap just pulls/pops off, there is a small filter under it, you can drive without that cap inplace to see if noise gets louder.
Pictures here: http://www.explorerforum.com/forums/...-w-pics.84220/
And this would be a vacuum leak.)
The computer operates the IAC Valve to maintain a target idle, based on engine temp.
Colder engine higher idle.
On start up(without touching gas pedal) the computer will have IAC Valve opened all the way, so RPMs should go high, then drop as computer closes IAC valve slowly to set engine temp based target idle.
If there is an air leak, vacuum leak, then computer would try to maintain the target idle while air flow was constantly changing, so you get fluctuating idle, computer is pretty good at maintaining a specific RPM within 15rpm of target, but that also means it can fluctuate alot with even a small vacuum leak, lol, its to precise for it's own good
Easy way to test for an air leak is to warm up engine to normal operating temp then let it idle.
Unplug the wires on the IAC valve, IAC Valve will close and idle should drop to 500 or engine may even stall, either is good it means no air leaks.
If idle stays at 700 or higher you have a leak.
The 4.0l SOHC engines had a common issue with PCV Valve hoses cracking at the elbows, on the underside where it would rub and it would be missed on normal inspections.
And the PCV system is, in general, a common vacuum leak source.
Move these(and other vacuum) hoses around while engine is idling, see if idle changes from a cracked hose being moved.