If it will run from holding the throttle slightly open but dies or will not start with your foot off the throttle, It is almost for sure the IAC. When it is acting up, try giving the IAC a rap with the handle of a screwdriver. Give it a smart whack, but not hard enough to dent or break the housing. If the problem goes away after the whack, you should try cleaning the IAC. If cleaning doesn't help, you will need to replace it.
