The IAV is a device that will blow air into the Cats during Idle. The IAV's ( if your Car has them now ) are located behind the Front Wheel in the fender.. IF the IAV's are not being used ( yours are not, as they are disconnected ) then ECU's ROM should be from a NON AIV ECU else the idle will be too rich.. in your case you need a TT ECU non AIV.. If you get a 'Replacement ECU' ( Jim Wolf or the Like ) the ROM Code will be the AIV Delete..