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What is the accelerator/what does it do?

The accelerator controls the flow of fuel into the engine which in turn controls the speed at which the engine rotates.

The accelerator consists of an accelerator pedal, an accelerator rod and an accelerator throttle cable. 

Getting into the details of the accelerator

The accelerator pedal manages the throttle valve which controls the flow of air into the engine. This dictates the amount of fuel released into the engine. By regulating the air and fuel flowing into the engine, the accelerator pedal controls the speed at which the car travels.  When you press down on the accelerator pedal, this causes the throttle valve to open up, allowing more air to flow in. The engine control unit recognises that the throttle valve is open and regulates the amount of fuel entering the engine in readiness for the increased flow of air. In essence, when you press the accelerator pedal with your foot, this makes the car go faster.  In a worse case scenario the accelerator pedal can malfunction and get stuck fast, but this is rare. Accelerator pedals do wear down over time, however, and you will eventually need to buy a new part for your car. Symptoms of this will include a sticky accelerator pedal or one that is harder to press down with your foot. A faulty accelerator pedal can get sticky when the throttle valve it connects to, which lets the air into the engine, gets clogged up with waste carbon. Generally speaking, if the compression of your foot on the accelerator pedal is not a smooth and easy process then you should ask your mechanic if it needs a replacement.

The accelerator pedal is linked to the throttle by the accelerator rod. The accelerator rod plays a major role in making sure the throttle valve is able to open fully and the flow of air and fuel in the engine is regulated. A good quality, fully functioning accelerator rod will enable smooth functioning of the accelerator pedal when you press your foot on it. Likewise, it should enable a steady, gentle spring return on the accelerator pedal when you release your foot. An old or worn out accelerator rod can cause problems by not producing adequate force to spin the throttle properly which prevents the throttle valve from opening sufficiently. This means the amount of fuel entering the engine of the car is not being regulated effectively, causing the accelerator pedal to stop working properly. If you are experiencing problems when using the accelerator pedal, seek advice from your mechanic about whether you need to buy a new accelerator rod.

The accelerator throttle cable links the car's accelerator pedal to the throttle. The accelerator throttle cable is made from steel cable protected by a casing. When you press your foot down on the accelerator pedal it causes the accelerator throttle cable to move which opens the throttle valve, allowing more air to run into the engine of the car. This is what ultimately causes acceleration.  Being the cable that joins the accelerator pedal to the throttle, the accelerator throttle cable is subject to a great deal of action, resulting in wear and tear and damage. The accelerator throttle cable can eventually erode from sustained use and will need to be changed with a good quality replacement.  If the accelerator throttle cable is run down or faulty you won't be able to control the car's acceleration properly. The efficiency of the accelerator throttle cable, therefore, is crucial in ensuring the engine is getting the correct amount of air and fuel, allowing control over the speed of the car. 

Some cars are fitted with a cruise control system, which is a function that takes control of the acceleration of the car. It does this by managing the flow of air into the engine and ultimately the speed the car travels at. When the accelerator pedal is pressed, this activates the cruise control vacuum pump. The cruise control vacuum pump works by creating a vacuum in the actuator, which operates the throttle valve. The throttle valve regulates the flow of air and fuel into the engine which determines the speed the car travels at, so the cruise control on the car takes charge of this process. Once the car has reached the desired pre-set speed, the cruise control system will maintain this constant speed and the cruise control vacuum pump shuts off. There is no need to press the accelerator pedal while cruise control is working as the system does all the work for you.