The throttle body is the TBI. It's the part that hold the throttle plates and what the throttle cable attached to and pulls on. On top of the throttle body, you will see the 2 electrical fuel injectors. Not sure if your boat is a DD or V-drive, but on car version of that unit, the IAC will be located on the drivers side of the TB.
It's not uncommon for them to gum up and stick causing low idle, stalling, high idle, etc. Take it out and clean it real good with a can of carb cleaner and an old tooth brush. That should fix any issue as this style IAC is pretty bullet proof and typically dont fail.