IAC wont cause that kind of problem. You can start the car without an IAC but it wont idle unless you give it gas. You sure it is your ECU making noise? Have you actually had someone put the key in and put your ear next to it listen? Also try resetting ECU if you haven't already. Any check engine lights? If you can get it to autozone, kragen, or some place like that, they will diagnose it for free. Or if you cant get it there, fork out 70 bucks (+/- a few bucks) use it, then take it back. If you see any codes that pop up and it just gives you a number ECU error codes can be found in the info and specs link at the top of the page. Let us know. All you can do is check everything. Check all connections around throttle body sensors and such. Don't go blowing money on stuff you may not need until you have tried anything and everything you and us on here can think of. Good luck and keep us posted. Good luck
Cameron