I am not by any means a mechanic but I do know a few things about my Neon. One thing I don't know and can't seem to find anywhere is, where is my IAC valve and is it difficult to replace?

The IAC is located on the throttle body - the unit is connected to the engine where the air intake hose connects. The throttle body has two sensors on it. The first is the throttle position sensor (TPS) which is always located on the opposite side of the butterfly valve arm to which the throttle cable connects. The other sensor is your IAC valve which is held on with a few screws. Both sensors are made of heavy plastic and have wires leading to them.

In general, IAC valves are little solinoids that move an arm and control an air valve. Usually, there are instructions on how to preset the lenght of that arm when installing one.

Now, I assume you are having an idle problem. Unless the computer specifically gave you the IAC code diagnostic, I wouldn't assume the problem is with the IAC value. The problem may be with the throttle body air passages being clogged with oily carbon build up. The IAC valve may just be sticking. This build up comes from the engine blowby thru the PCV value - it gets everywhere. You should try a can of carberator cleaner thru the throttle body first.