What Is a Throttle Body?

by Richard Rowe

Internal combustion gasoline engines require three things to operate: oxygen, fuel and a spark. On modern engines, fuel delivery and spark timing are handled by a computer controlled system of pumps and actuators. Air delivery is a bit more analog, which is where the throttle body comes in.


Man working on engine

Throttle bodies are essentially air valves, and can take a number of forms. Most are butterfly valves, but barrel-type and pinch valves have also been used.


Open hotrod engine

Prior to fuel injection, air delivery was modulated by a set of butterfly valves set into the base of an engine's carburetor.

MFI Throttle Bodies

Car engine

Most engines use Multi-Point Fuel Injection (MFI.) In these systems, the throttle body is responsible only for modulating air delivery.

TBI Systems

Mechanic working on engine

Many older engines use Throttle Body Injection (TBI.) These throttle bodies resemble carburetors, and utilize one or a pair of fuel injectors mounted atop the assembly, which shoot fuel through the butterfly valves and into the engine.

Idle Air Control

Mechanic working on engine of car

On most engines, the throttle body also contains a secondary circuit to control airflow at idle. This channel is called the IAC (Idle Air Control), and utilizes a computer-controlled valve to vary airflow.

About the Author

Richard Rowe has been writing professionally since 2007, specializing in automotive topics. He has worked as a tractor-trailer driver and mechanic, a rigger at a fire engine factory and as a race-car driver and builder. Rowe studied engineering, philosophy and American literature at Central Florida Community College.

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