No, IAC Valve doesn't close all the way when unplugged/unpowered
It only moves 3/8" when fully opened, so not a lot of movement when it is working
But it doesn't take much air increase or decrease to raise or lower RPMs on a running engine
Warm up engine first, 5min or so
Let it idle
Unplug IAC Valve, RPMs should drop to 500-600, barely running or engine may even stall, either is good it means computer using IAC Valve was controlling idle RPMs
If idle doesn't drop it means IAC Valve is stuck or RPMs are higher than computer can control
i.e. idle is 950rpms, computer closes IAC valve all the way but it can't get it lower than 950 usually because of a vacuum leak
With IAC Valve still unplugged and a high idle, start unplugging vacuum lines on the intake and plugging port with finger, see if idle will drop
Warm engine Target idle on a 4cyl engine manual trans is usually about 750-800rpms
Automatic 800-850rpms
On cold start if RPMs are 1,100+ then IAC Valve is working, cold engine needs Choke and higher RPMs, but idle RPMs should slowly drop over the next 5min, to warm engine target idle
Cold target idle is based on outside temp so varies through out the year, the colder the temp the higher the idle
Which is why you want to test on warmed up engine to eliminate the variables
With IAC Valve off and unplugged turn on the key, computer will send 11-12v to IAC Valves wires, you can test that with volt meter
The red wire will have Battery Volts if test to engine ground
The other wire comes from computer and is a variable ground, that's how the voltage is controlled, thru ground side not the 12volt side
Plug volt meter into the 2 wires and see what voltage is, 11-12v
Watch the valve in IAC Valve and plug connector back in, valve should move slightly, if not it may be dead, assuming you had 11-12v on above test
You can move the valve with screwdriver when its unplugged, then try moving it with it plugged in, should be hard to move when plugged in
Motorcraft or Hitachi brand IAC Valves are the only ones that work well on out Rangers, other brands will cause odd issues with idle