Has the throttle idle screw been adjusted,ie the engine is having too much air at idle,giving the wrong idle speed which the IAC valve is now trying to control, via the ECU.
What is the voltage out of the throttle position sensor @ ign on, engine OFF, should be below 1volt. i.e. .95V
My engine has always stopped when taking the pipe off the IAC, you need to have the live data to check what this valve is doing.