I've seen this many times, what happens is that the idle valve gets stuck and then the idle control unit gets fried so the idle gets wacky. Here's a quick test, unplug the idle valve and check if you get voltage from the connector, if you do that means the idle cpu is still good, then unbolt the idle valve, and take it off. Now look for the two connections on the idle valve, and connect one to the + and the other to the - of the battery, if the idle valve is still good it will close shut as soon as it gets voltage (you can hear a click and you should not be able to blow air through the air passages.)
If you don't get voltage to the idle valve and the idle valve doesn't snap shut when you connect it to the battery, replace both of them.
If the valve works and you're not getting voltage to the idle valve from the idle cpu, well thats a little more complicated to figure out because the idle cpu has sensors all over the engine to check temp and rpms and its a real pain in the @$$ to diagnose, start with the easiest first, and good luck!