What is a Throttle?

Katharine Swan

A car’s throttle is essentially what controls how fast the engine goes, and therefore how fast the car goes. The throttle is usually a butterfly valve assembly on the intake manifold, and is connected to the accelerator, or gas pedal, via the throttle linkage. This linkage enables you to control the engine’s throttle by how far you move the gas pedal — the further down you press the gas pedal, the more the throttle opens.

Pressing a car's gas pedal increases the throttle opening.
Pressing a car's gas pedal increases the throttle opening.

Many people hold the misconception that the purpose of the throttle is to control the amount of fuel going into the engine. In fact, it is the exact opposite: the throttle controls the amount of air that goes into the engine.

A carburetor ensures the proper mixture of gasoline and air enters an engine for combustion.
A carburetor ensures the proper mixture of gasoline and air enters an engine for combustion.

An internal combustion engine runs on the force of exploding fuel and air. However, to generate the proper explosion in the combustion chambers, there needs to be a very specific mixture of vaporized fuel and oxygen. Therefore, in an internal combustion engine, there are several systems in place to regulate the air/fuel ratio.

In a carbureted car, the carburetor uses very simple principles of vacuum to maintain the correct air/fuel ratio. In a fuel injected car, on the other hand, the air flow meter, oxygen sensor, and the computer that run the electronic fuel injection all work together to ensure that the engine gets the right amount of both air and fuel. There are two different kinds of electronic fuel injection: throttle body injection, which works more like a computerized version of a carburetor, and multiport injection, which features a separate fuel injector for each cylinder.

Whether the car is carbureted or fuel injected, when the throttle opens, more air rushes into the engine. At the same time, the intake and fuel systems compensate by adding more fuel to the mixture. In other words, the throttle directly controls the amount of air that enters the combustion chambers, which indirectly affects the amount of fuel that enters the chambers.

You might also Like

Readers Also Love

Discussion Comments


A good explanation has been provided which can easily be understood by anybody interested in the subject.


When I think of a throttle I think of the way it has worked its way into the popular imagination as a symbol of speed or power. You think of roaring motorcycles racing down the highway or fighter jets screaming past the speed of sound. Even though the throttle is just one part of what make machines travel fast, it has become the primary symbol of mechanical speed and power.


This article got me thinking about what has always amazed me about cars. They are essentially huge collections of simple machines with very specific tasks working together to accomplish a very difficult and complicated goal.

The throttle is a pretty simple concept. It opens up more or less to regulate the amount of oxygen. But this simple process working in concert with lots of other simple processes allows us to get huge pieces of metal weighing thousands of pounds to go from 0-60 MPH in a matter of seconds. Engineering is amazing


Wow, thanks for this explanation. It appears that I was making a common mistake. I always thought that the throttle controlled the amount of fuel going into the engine. As you pointed out, it is just the opposite.

I am not a mechanic or someone who loves cars, but it is still nice to understand a little bit about how they work. I have a feeling that this little piece of knowledge will serve me well one day.

Post your comments
Forgot password?