Engine will not idle after installing an aftermarket IAC valve?

Sounds like a bad valve. Those should be a simple, unplug, unbolt, replace valve and gasket and plug in the connector. Then disconnect the battery or reset the idle with a scan tool. Once that is done you might have to play with the throttle a bit until it learns the idle again. If it's stuck open though then it's bad. These days that isn't uncommon to find new parts that are bad. I would try to drive it around a bit and see if it possibly resets. If it doesn't after a couple miles of stop and go traffic, then replace the valve again.
What was the reason for replacing the original?