Q: What's the difference between idle control valve and auxiliary idle air control valve

asked by on September 13, 2017

What is the difference between an idle air control valve and an auxiliary idle air control valve.

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The idle air control valve monitors the air intake as it is mixed with fuel prior to being injected into the engine at low speeds and at idle. This valve is controlled by the vehicle’s computer and will adjust idle speed based upon other measurements such as engine temperature, intake air temperature and electrical system load or voltage. This is also an important function when starting the motor as it allows the motor to run and idle on it’s own once the motor fires. When you accelerate, the engine RPM increases, and as you let off the gas, the RPM slowly returns to the normal idling speed with the help of the idle air control valve making the transition from a higher RPM back down to idle speed while adjusting the air/fuel ratio constantly to allow this to happen smoothly. When the engine RPM drops below the normal range of about 750-800 RPM, this often times will cause the engine to stall indicating a dirty or faulty idle air control valve.

The auxiliary idle control valve, also known as a cold start valve or cold start injector works to maintain a proper idle when the motor is cold. The idle control valve described above works during normal operating temperatures. The cold start injector or cold start valve injects more fuel into the motor until the engine reaches a specific operating temperature. The computer simply feeds a little extra fuel through the fuel injectors to start the engine and then maintains a certain amount of fuel supply to the motor until it is warm.

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