Here'* a few things you might want to check.
Did you reset the computer and do a re-learn after you changed the IAC? Also, check the routing and condition of vacuum lines; it'* possible something came loose or a line cracked while you were under there. It probably wouldn't hurt to check for a sticking throttle body, or a dirty MAF. Make absolutely sure if you clean your MAF sensor, *ONLY* use MAF Sensor Cleaner, and make sure it has air-dried completely before starting the car.
The MAF may be an issue too, try disconnecting it (ignition off) and start it and see what happens. Usually a MAF failure will cause rough idle or no-start, but this is an easy way to rule that out.