What is engine idle speed and what are they for

The movement of the car is ensured by the correct operation of all electronic and technical units of the vehicle, including the correct operation of the idle speed. Despite the seeming simplicity, keeping the engine RPM in optimal mode is a complex electro-mechanical process, without which it would be impossible for a car to start up as easily as it does every day on all modern cars in the world.

What it means to idle a car

Idling has more than a century of history in the development and modernization of carburetor and injector injection mechanisms. Surprisingly, in the first cars, the very concept of idling as such did not exist, as well as there was no familiar range of operating revolutions, which were limited to 250-500 inconsistent engine revolutions. Cars first began to be equipped with adjustable idle speed only in 1915.

In modern cars, no-load operation of the engine is provided by the idle speed regulator, or idle speed sensor. The device is a valve integrated into the engine throttle. It is regulated by controlled air flow through the valve bypassing the damper, which is in the closed position without engine load.

If cars didn’t have idle speed, they would be as clumsy as turtles and would have virtually no additional functions. The fact is that without a load, a running engine continues to power the car by turning the alternator, spinning the fuel and oil pump, which maintain the vital engine cycles, and make accurate operation of the ignition system possible.

If one were to imagine a car without idling, its engine would have to undergo critical overloads when trying to start, with high torque achieved before the cylinder walls had time to properly lubricate with oil and heat up to operating temperature.

Such an engine operation scheme is only possible on hybrid cars, where all devices are powered by an electric motor. The main engine assumes the load only after acceleration to a certain speed, when the operating temperature has already been reached and the lubricating properties of the engine have been achieved.

What are the functions of the engine idle speed

Engine idle speed plays an important role in the movement of the car and is strongly influenced by the type and quality of the fuel mixture. The number of engine idle revolutions is directly affected by the rate of fuel combustion. For example, gasoline engines will idle between 800 and 1,000 rpm and diesel engines will idle between 500 and 800 rpm.

The idle speed regulator has several very important functions:

  1. to ensure that the engine warms up evenly during initial startup (when cold).
  2. To increase the RPM of the engine, which has not yet had time to warm up, but started running under load.
  3. To reduce the time for the engine to gain maximum torque. In cars with hybrid engines, this function is performed by the electric motor.
  4. Spin up the engine at the same time as increasing the power consumption in order to provide normal electric power to all devices of the car and to relieve the load on the generator. For example, when you turn on the heater, stereo or high beam headlights, the engine idle speed will automatically be increased.
  5. Maintain engine speed without load within specified limits.
  6. Maintain revolutions when releasing the accelerator pedal sharply and emergency braking to prevent the engine from stalling.
  7. Avoid the possibility of a lean fuel mixture which can cause serious engine damage.

An integral part of the idle speed regulator is the bypass air channel, or bypass. The working elements of the IAC can be called a process port, which is closed or opened by means of a needle valve.

The movement of the needle is ensured by a stator, where the needle acts as a rotor, or an electromagnetic winding, where the rotor is moved by electromagnetic forces. The actuating mechanism may also be in the form of a solenoid, which opens or closes the regulator’s damper when voltage is applied.

Main malfunctions of the idling mechanism in the car

The engine RPMs specified by car manufacturers are optimal and allow the engine to consume a minimum of fuel, while not clogging the combustion chambers with exhaust deposits and emitting the cleanest possible exhaust into the atmosphere.

In many respects the engine idle speed depends on the specifics of the power unit and its oil pump in particular. Thus, in order to ensure normal lubricating properties of the cylinder walls, the car electronics will maintain a certain number of revolutions at idle speed.

Proper operation of the car at idle speed, in turn, depends not only on a functioning idle speed regulator, but also on many other causes. Thus, floating revolutions, as the most common idling speed problem, may be a consequence of:

  • malfunction of the ignition system;
  • contamination of the fuel system;
  • malfunction of a choke sensor and a choke itself;
  • air drainage as a result of depressurized air hoses;
  • severe contamination of the air filter;
  • malfunction of electrical wiring;
  • malfunction in the electronic control unit.

Troubleshooting of the VTC can be determined by a few simple signs. If the engine RPM does not increase, or it involuntarily increases or decreases when increasing the load on the electrical network of the car, it is possible to speak about the sensor failure.

Other common signs are the engine stalling when trying to start and low RPM when the engine is cold.

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