Throttle body introduction and defects

 Throttle body in gasoline engine

What does throttle body and how it works?

The first part of a gasoline engine through which air is sucked in the engine is the throttlebody.

Engine is basically an air pump. It sucks air, ignite fuel in it and discharge the air through tail pipe. Throttle body is the essential part of a gasoline engine in the air intake system where the throttle body controls the intake air to the engine. A throttle body is a butterfly valve in a housing where it is mounted on a shaft. The butterfly valve can be rotated through a mechanical linkage cable or through a servo motor electrically. The motion of the butterfly valve is registered to the ecu or car computer through a sensor known as throttle position sensor or TPS.

Mechanical linkage type or old style throttle body

When the gas pedal or accelerator pedal is pushed the butterfly or throttle plate inside the throttle body is opened and allows the air to the engine cylinder or combustion chamber. When the gas pedal is depressed, the butterfly valve or the throttle plate closes and it restricts the air flow to the engine. By this way the quantity of air is controlled to the engine and hence the engine or vehicle speed is controlled.

How Throttle body Works

Throttle body is located in between the air filter and air intake manifold of an engine. The butterfly valve or the throttle plate inside the throttle body precisely control the air intake to the engine. The quantity of the air regulates the air fuel mixture to the gasoline engine. The engine needs air fuel mixture in a stoichiometry level of 14.7:1 for proper ignition and optimum performance. If this stoichiometry level is not maintained, the optimum operation and the performance can’t achieve. Throttle body controls the air fuel ration very precisely all the time manually by mechanical wire linkage or electronically through ecu or computer.

Motorized throttle body

Idle air control value or IAC associated with throttle body

The throttle body consists some more systems like IAC or idle air control valve which is used to regulate the idle running of the vehicle. The IAC valve was used on old style throttle bodies which were using a mechanical linkage cable to activate the throttle plate or the butterfly plate inside the throttle body. IAC valve or idle air control valve function is to retain the vehicle in start condition at idle running conditions at 600 rpm all the time in all circumstances. The IAC valve or the idle air control valve automatically regulates the engine speed to 600 rpm when air conditioner compressor kicks on and the vehicle is stopped at signals or in parking area start at idle speed and people sitting inside.

IAC or Idle air control valve

The newer throttle bodies don’t use the mechanical linkage cable. Instead they use a servo system controlled by engine control unit of ecu to regulate the air intake through throttle body. These new throttle bodies controls or regulates the air intake at idle through main throttle plate or butterfly valve. Their control is very precise as in such new throttle bodies the throttle plate or the butterfly valve is not directly controlled through the driver foot but it is controlled by ecu or engine control module.

Problems with throttle body and their Solutions

Throttle body common defect is dust accumulation inside the throttle body or the IAC valve or idle air control valve. As 10000 liters of air is required to burn 1 liter of petrol. All this air is passed through the throttle body. Although there is a filter located before the throttle body but still air contains very fine particles of air which could be accumulated inside the throttle body and they create issues in air regulation especially idling become poor and rough if a throttle body accumulated dust inside. The dust accumulation is not a very quick process and it depends upon your environment where you drive your car and how often you drive your can in routine. The solution to this problem is to clean and wash the throttle body after certain period of time.

Other problem could be a worn out throttle plate spindle bushings or bearings. In some cases there bushings could be replaced and in most of the cases the whole throttle body is replaced with a new one. Although this defect is very seldom and not very common.

In some cases you will see defective temperature sensor at throttle body. The sensor could be failed sometimes due to aging and mostly due to some other loose connection somewhere in the car wiring. In such a case the sensor replacement and the loose connection repair could solve the defect.