Throttle Body: Description and Operation

Throttle Body Injection (TBI) Unit:

DESCRIPTION
The Throttle Body Fuel Injection (TBI) unit consists of the main bore, air and/or fuel passage, vacuum passage (for Manifold Absolute Pressure [MAP] sensor, Evaporative Emission [EVAP] control system and Exhaust Gas Recirculation [EGR] system), air induction passage and the following parts.

^ Fuel injector which injects fuel according to the signal from the Powertrain Control Module (PCM).
^ Fuel pressure regulator which maintains the fuel pressure to the fuel injector a certain amount higher than the pressure in the intake manifold.
^ Throttle valve which is interlocked with the accelerator pedal and controls the amount of air/fuel mixture drawn into the combustion chamber.
^ Idle Speed Control (ISC) motor which controls minimum throttle valve position (opening) to adjust engine idle speed.
^ Throttle Position (TP) sensor which detects the throttle valve opening and sends a signal to the PCM.

Legend
1. Fuel Injector Cover
2. Fuel Injector
3. Upper O Ring (Large)
4. Fuel Pressure Regulator
5. Upper TB Unit
6. Lower O-Ring (Small)
7. Vacuum Nozzle
8. Throttle Valve
9. Lower TB Unit
10. ISC Motor