Throttle Body

Throttle Body
Throttle Body

The throttle body is where the air actually enters your vehicles engine. When you give your vehicle gas, a blade or "Butterfly" as it is known, opens according to how much throttle you give and allows air to enter the intake manifold. Throttle bodies are located at the inlet of the intake manifold and are connected to the air filter. Fuel injected engines use an air metering system that is measured by either airflow, Mass Air Flow Meter- MAF or by manifold pressure-vacuum, Manifold Absolute Pressure sensor- MAP, both of which are affected by the amount of throttle applied. Another sensor that is directly related to the throttle body s the throttle position sensor TPS, this sensor is mounted directly on the end of the throttle shaft and tells the computer exactly how far the throttle has been opened.

Some vehicles don t have a throttle position sensor, these are called "Drive-By-Wire", which mean there isn't actually a throttle cable that attaches the gas pedal to the throttle body. Drive by wire vehicles use a throttle position sensor at the gas pedal and an electric motor mounted on the throttle body, which acts as the throttle cable and the idle speed controller, by using input from the gas pedal position sensor to tell the throttle body how far to open.

Over time the throttle body in your vehicle can become gummed up with coking, which is a natural by-product of internal combustion engines. This coking in the throttle bore can cause low or unstable idling of your engine or even hard starting. The throttle plate (butterfly) lets a pre-determined amount of air into the intake around it, when the coking takes away this air; the computer has to compensate which can cause the issues mentioned. Some manufacturers use special coatings inside the throttle bore, so when cleaning them do not use harsh chemicals such as carburetor cleaner or brake cleaner. These vehicles will have stickers that warn of the coatings used. All other vehicles you can simply use some carburetor cleaner on a rag and clean around the throttle plate while someone holds the gas pedal down for you.

Throttle bodies will generally last a very long time; there are no real wearing parts other than the bushings that support the throttle shaft. The throttle position sensor will usually bolt on the side, so they are replaceable separately. If your vehicle is drive by wire (no throttle cable) and there is an issue with the motor on it, you will have to replace the entire unit. This is a fairly simple job, although sometimes a relearn procedure is required to obtain idle and set the full throttle parameters, refer to a shop manual for your vehicle for the proper relearn procedures.

Larger aftermarket throttle body units have found their place among modern hot-rodders. These units will allow more air into the intake due to larger butterflies in them. When installing a larger throttle body, be advised that if no modifications are made to the intake system before the throttle body, the performance gains may not be as noticeable as expected. The factory size throttle bodies are a matched to the rest of the system to create the most power and economy possible. Some of the aftermarket units will omit the coolant lines that keep the throttle body from freezing up at cold ambient temps to keep the intake temperatures down, which in turn makes more power. When replacing you throttle body for whatever reason, use an OEM (Original Equipment Manufacturer) or equivalent part to ensure proper fit and performance.

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Written by
Co-Founder and CEO of
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-08-19)