Throttle Body Unit (TBI) – The throttle body takes the place of a carburetor. The TBI unit usually sits on top of the intake manifold and the primary function is to combine the fuel and air together to form just the right air to fuel mixture. The throttle cable connects the accelerator pedal inside the vehicle to the TBI unit.
A dirty throttle body (Especially worse on Ford products) can cause rough or erratic idle speeds and stalling at idle. This carbon build up at the inlet of the TBI unit can cause the throttle vane to stick thus producing the above problems.