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An idle air control actuator or idle air control valve (IAC actuator/valve) is a device commonly used in fuel-injected vehicles to control the engine's idling rotational speed (RPM). [1] In carburetted vehicles a similar device known as an idle speed control actuator is used.
The IAC actuator is an electrically controlled device, which gets its input from the vehicle's engine control unit (ECU). The actuator is fitted such that it either bypasses the throttle or operates the throttle butterfly valve directly. The actuator consists of a linear servo actuator servomotor that controls a plunger which varies air flow through the throttle body. The position of the servomotor and hence the amount of air bypass is controlled digitally by the engine ECU. This allows the engine's idle speed to be maintained constant. The linear servo is most commonly a combination of a DC motor, lead screw and a digital optical encoder.
There is essentially no difference in efficiency between the technique of bypassing the throttle butterfly and operating the butterfly itself. The IAC allows the ECU to maintain minimum RPM irrespective of changes in engine load, sometimes referred to as anti-stall feature. Thus the driver can more easily move the car from stand-still by merely releasing the clutch (manual transmission) or the brake (automatic transmission) without having to simultaneously press the accelerator.
Although the IAC is supposed to last the vehicle's lifetime, various reasons may cause it to fail/malfunction prematurely. The most common failure mode is partial/complete jamming of the actuator (due to dirt/dust or even oil) where it cannot be smoothly controlled. The result is an engine that fails to maintain idle RPM and frequently stalls. A jammed actuator may be freed simply by cleaning it. However an actuator that has stopped working due to a fault in its servomotor will need replacement.
Air leaks in either the stepper housing or pipes will cause elevated idle RPM.
A carburetor is a device used by a gasoline internal combustion engine to control and mix air and fuel entering the engine. The primary method of adding fuel to the intake air is through the Venturi tube in the main metering circuit, though various other components are also used to provide extra fuel or air in specific circumstances.
Cruise control is a system that automatically controls the speed of an automobile. The system is a servomechanism that takes over the car's throttle to maintain a steady speed set by the driver.
Engine tuning is the adjustment or modification of the internal combustion engine or Engine Control Unit (ECU) to yield optimal performance and increase the engine's power output, economy, or durability. These goals may be mutually exclusive; an engine may be de-tuned with respect to output power in exchange for better economy or longer engine life due to lessened stress on engine components.
An automatic transmission is a multi-speed transmission used in motor vehicles that does not require any input from the driver to change forward gears under normal driving conditions. Vehicles with internal combustion engines, unlike electric vehicles, require the engine to operate in a narrow range of rates of rotation, requiring a gearbox, operated manually or automatically, to drive the wheels over a wide range of speeds.
An electronic control unit (ECU), also known as an electronic control module (ECM), is an embedded system in automotive electronics that controls one or more of the electrical systems or subsystems in a car or other motor vehicle.
A manual transmission (MT), also known as manual gearbox, standard transmission, or stick shift, is a multi-speed motor vehicle transmission system, where gear changes require the driver to manually select the gears by operating a gear stick and clutch.
Engine braking occurs when the retarding forces within an internal combustion engine are used to slow down a motor vehicle, as opposed to using additional external braking mechanisms such as friction brakes or magnetic brakes.
A wastegate is a valve that controls the flow of exhaust gases to the turbine wheel in a turbocharged engine system.
Manifold vacuum, or engine vacuum in an internal combustion engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere.
An engine control unit (ECU), also called an engine control module (ECM), is a device which controls multiple systems of an internal combustion engine in a single unit. Systems commonly controlled by an ECU include the fuel injection and ignition systems.
A rev limiter is a device fitted in modern vehicles that have internal combustion engines. They are intended to protect an engine by restricting its maximum rotational speed, measured in revolutions per minute (RPM). Rev limiters are pre-set by the engine manufacturer. There are also aftermarket units where a separate controller is installed using a custom RPM setting. A limiter prevents a vehicle's engine from being pushed beyond the manufacturer's limit, known as the redline. At some point beyond the redline, engine damage may occur.
A transmission control unit (TCU), also known as a transmission control module (TCM), or a gearbox control unit (GCU), is a type of automotive ECU that is used to control electronic automatic transmissions. Similar systems are used in conjunction with various semi-automatic transmissions, purely for clutch automation and actuation. A TCU in a modern automatic transmission generally uses sensors from the vehicle, as well as data provided by the engine control unit (ECU), to calculate how and when to change gears in the vehicle for optimum performance, fuel economy and shift quality.
A throttle is a mechanism by which fluid flow is managed by constriction or obstruction.
Digifant is an Engine Management System operated by an Engine Control Unit that actuates outputs, such as fuel injection and ignition systems, using information derived from sensor inputs, such as engine speed, exhaust oxygen and intake air flow. Digifant was designed by Volkswagen Group, in cooperation with Robert Bosch GmbH.
Trionic T5.5 is an engine management system in the Saab Trionic range. It controls ignition, fuel injection and turbo boost pressure. The system was introduced in the 1993 Saab 9000 2.3 Turbo with B234L and B234R engine.
Electronic Diesel Control is a diesel engine fuel injection control system for the precise metering and delivery of fuel into the combustion chamber of modern diesel engines used in trucks and cars.
A motorcycle transmission is a transmission created specifically for motorcycle applications. They may also be found in use on other light vehicles such as motor tricycles and quadbikes, go-karts, offroad buggies, auto rickshaws, mowers, and other utility vehicles, microcars, and even some superlight racing cars.
Car controls are the components in automobiles and other powered road vehicles, such as trucks and buses, used for driving and parking.
SECU-3 is an internal combustion engine control unit. It is being developed as an open source project. Anyone can take part in the project, and can access all the information without any registrations.
Gliding is an energy-efficient driving mode achieved by turning off the internal combustion engine while the vehicle is still moving in order to save fuel. This is differentiated from coasting, which means running the vehicle in idle mode by disengaging the engine from the wheels, either by disengaging the clutch or setting the transmission or gearbox to neutral position. Gliding and coasting use the accelerated kinetic energy reserve stored in the vehicles mass, i.e. inertia, to keep the vehicle moving. This energy, however, is being lost due to forces that resist movement, such as air-drag, rolling resistance and gravity. The functionality, being an integral concept of hybrid electric vehicles, is performed automatically by the engine controller. For vehicles with a conventional internal combustion engine, coasting can be performed manually; gliding requires having a gear box. Manual gliding or coasting is illegal in some states. An extra button to stop the engine was shown in 1979 on International Motor Show Germany, but never became a feature in mass production of any vehicle. In 1980 research was made on the IRVW II. A so-called eClutch uses an actuator to disengage the clutch when the driver releases the accelerator.