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What is a Throttle Body?

In the automotive industry today, two main types of engines exist; the electric and the internal combustion engines. While the electric engines rely majorly on motors, the internal combustion engines rely on combustion. For the combustion of fuel to take place and drive the engine, there must be oxygen; thus, there is a need for an air intake system in an internal combustion engine. The throttle body is part of the air intake system in an internal combustion engine such as the gasoline, petrol, and diesel engine. You can locate the throttle body between the manifold and the air filter, and it regulates the air inflow. 

Functions of a throttle body

The throttle body has two functions regulating the amount of air in and to control the temperature of the air flowing in. It regulates the temperature using the engine coolant line that runs through it that either cools or warms the air to a given temperature. The air of a given temperature has a known density, and this facilitates the injection of a specific amount of fuel for the right air-fuel ratio. 

 The throttle body regulates the amount of air flowing into the engine by how wide the throttle plate opens. The wider the throttle plate opening, the more the amount of air intake. 

How does the throttle-body work?

The throttle body has two air inlets; the primary and the secondary inlet. The secondary air intake is a smaller bypass of the main throttle that allows air in when the engine is idling. It has the Idle Air Control Valve (IACV) that is a solenoid driven valve, used by the ECU to control air inflow allowing the engine to idle. During idling, the throttle plate is shut entirely letting in no air. As a result, without the bypass, the combustion would stop, and no idling would be possible.

The Primary inlet, on the other hand, is the central air intake that starts operating when the driver pushes on the accelerator. When the gas pedal is pushed down to accelerate, the throttle plate, also known as the butterfly, opens up allowing more air to the engine. The harder the acceleration, the wider the opening and on releasing the gas pedal, the plate closes the opening choking off airflow into the combustion chamber. The throttle body communicates with the accelerator via the throttle cable for the older car model or electronically via sensors in the new vehicle models. 

The mounting of the throttle bodies can be:

  1. Single throttle body per engine -  this is common in standard vehicles where one throttle body serves the whole engine.
  2. Multiple throttle bodies per engine - where more than one throttle body is employed and are linked together to function simultaneously. 
  3. Individual throttle body (ITBs): this is standard in higher-performance cars and motorcycles where each combustion cylinder has its separate throttle body.

Image of BMW S65 from the E92 BMW M3 showing eight individual throttle bodies

The different types of throttle bodies 

The throttle bodies can broadly be classified into three depending on how the throttle body is controlled or communicates with the accelerator 

  1. Mechanically controlled throttle bodies - the throttle body is controlled using the throttle cable that connects to the accelerate
  2. Mechanically/electronically controlled - the throttle body is semi-controlled by a cable where also the sensors play a vital role in controlling the opening and closing of the.
  3. Electronically controlled - the control of the throttle body is primarily by sensors (Fly by Wire)

Issues with throttle body 

The common problems with throttle bodies include

  1. Faulty temperature sensor on the throttle bodies
  2. Faulty connections of the electric wires connecting the throttle body temperature sensors and the ECU on the dashboard.
  3. Vacuum leak - the vacuum pipe that draws in the air may have a hole
  4. A build-up of carbon on the throttle body
  5. Breaking of the drawback spring that crosses the butterfly valve
  6. A build-up of dirt inside the housing
  7. Corrosion of the throttle body parts
  8. Loss of the primary throttle setting

Symptoms of a faulty throttle body

 When the throttle body is flawed, distinct signs appears that include:

  • Rough idling and idle surges - the irregular intake of air causes rough idling and surges at times.
  • Dashboard check engine light - the car sensors are likely to detect the majority of the issues with the throttle body and give a warning
  • Poor engine performance - the vehicle loses power due to inadequate air supply for optimal fuel combustion
  • Jumping RPM - likely to be caused by faulty wiring or vacuum leaks
  • Engine stalling down despite the vehicle having fuel and battery charged fully
  • A noticeable change in fuel consumption
  • Annoying surges in speed when accelerating or hesitation while pushing on the accelerator 
  • Jerking /bucking when you engage the gear. In some cases, changing the gear becomes difficult as the vehicle lacks the power to drive in next higher gear.

Possible causes of a malfunction

The above-mentioned symptoms have of course an underlying cause. One of the main causes of a malfunctioning throttle body is internal contamination. Due to the contamination accumulated in the throttle body, the throttle valve can no longer move properly, causing problems with the control of the air supply.

Another cause for a malfunctioning throttle body is the presence of one or more vacuum leaks. This causes 'false air' to be sucked in, so that the total amount of air sucked in does not correspond to the position of the throttle valve.

An incorrectly adjusted throttle position sensor can also cause an engine to run badly

Do you have a new throttle body that you would like to change? Take a look at our complete description of the throttle bodies at SPELAB shop. There is a good chance that you will find the desired type of throttle body with us within a few clicks.


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