The PCM drives the IAC via a DC duty cycle. So applying 12 volts across the IAC should make it open 100%. However don't expect it to behave like a solenoid and "click", Further if this is the black vented version (which a 1999/2000 should have), it's doubtful that a "blow on it" test will work. Why? Because the IAC needs engine vacuum to make the black vent close.
The limits of the test should be to apply 12 volts to the IAC while the motor is running. This should make the RPM's rise a bunch. Maybe even to over speed.