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The idle speed regulator (idle speed sensor, IAC) is a device for automatic stabilization and adjustment of idle speed. This idle speed sensor is often an electric motor that has a tapered needle.

The purpose of the IAC is to supply the amount of air necessary for stable engine operation, bypassing the throttle valve at idle speed. In other words, if the engine is idling, the throttle is closed. In this case, air enters the internal combustion engine through an additional channel. Adjustment of idle speed becomes possible due to a change in the cross-section of this channel, which overlaps the idle speed sensor needle.

The principle of operation of the idle speed sensor (IAC) is as follows. The amount of incoming air is determined by the airflow meter of the DMRV, after which the engine ECU receives the corresponding signal and supplies the required amount of fuel through the injection nozzles. The ECU also considers the readings of the DPKV (crankshaft position sensor), thus determining the engine speed in different operating modes. In parallel, the electronic control unit of the internal combustion engine controls the operation of the idle speed controller. After the engine reaches idle speed, the idle speed controller IAC, under the control of the ECU, slightly opens the additional channel so that the required amount of air is supplied to the engine to maintain the specified idle speed of the engine.

IAC also changes idle speed depending on the degree of warming up of the power unit. If the engine is not warmed up to operating temperatures, the ECU sends a signal to the IAC; the regulator increases the flow area of ​​the additional channel. As the amount of air increases, the control unit increases the fuel supply, increasing the idle speed. At higher rpm, the engine warms up faster.
Similarly, the ECU also compensates for changing loads on the engine in idle mode (turning on headlights, heating mirrors or seats, connecting an air conditioner and other power consumers.) Thanks to the synchronous operation of the ECU and the IAC actuator, it is possible to increase or decrease the incoming air around the throttle dynamically. As a result, the engine runs stably at idle speed.

Idle sensor malfunctions usually show up as the following symptoms:

  • the engine will not start;
  • the engine idles unstable;
  • rpm float “cold” and / or “hot”;
  • there is an independent increase or decrease in idle speed on a warm engine;
  • after entering the idle mode, the engine stalls;
  • when starting a cold engine, the speed does not increase to warm up;
  • idle speed falls after turning on energy consumers (dimensions, headlights, air conditioning, heating, etc.);
The indicated malfunctions of the idle speed control can manifest themselves both individually and in combination. Note that the “check” on the dashboard is usually off in case of problems with the IAC. Also, malfunctions of the idle sensor are reminiscent of the symptoms of a breakdown of the throttle position sensor (TPS). At the same time, failures in the operation of the TPS are accompanied by the “check” lighting up.

To accurately determine the breakdown, it is necessary to check the idle speed regulator. After removing the IAC for diagnostics, cleaning or replacement and its subsequent installation, it is necessary to calibrate the device. To do this, before installing the regulator, you will need to remove the terminal from the battery. After installing the device, the terminal returns to its place, then for 10-15 seconds. The ignition is turned on without starting the engine. At this time, the ECU is calibrating the IAC. Please note that the electronic control unit will not calibrate the regulator without removing the terminal from the battery. Then You should start the engine to check the operation of the idle speed controller with the engine running.

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