throttle body lower half is the ISC unit....
intended injectors means injector size suitable for ur engine displacement and capability... lets say u stroked ur engine up to 1.6 but still running 145cc injector from 1.3 engine, it will not be sufficient especially high revs....
on the other hand if u install too big injectors (for example 390cc gsr injector in 1.3L engine), u will have idling problem and high fuel consumption....
1 thing most important, if u intend to put bigger cc injectors, its best to have a piggyback ecu to control the amount of fuel injected per cycle...