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Unlike a Multi-Port fuel injection system (MPI) which uses eight injectors mounted in the manifold runners, a Throttle Body Injector (TBI) mounts on top of a normal intake manifold and functions very similar to a carburetor. The four injectors hang just above the throttle blades, which open using a familiar-looking Holley linkage, but it's not the same as a carb linkage. The biggest difference between any TBI and a carb are all the wires going into it. There are connections for the Throttle Position Sensor (TPS), Idle Air Control (IAC), Manifold Air Temp (MAT) sensor, and injector harness, just to name a few.