- throttle potentiometer - informs the electronic control unit about the position of the throttle and the speed of closing / opening the throttle;
- coolant temperature sensor - informs the control unit about the engine temperature;
- air flow sensor - informs the control unit about the amount and temperature of air passing through the intake air duct;
- crank angle sensor (installed in the ignition distributor) - informs the control unit about the speed of the engine and the position of the crankshaft;
- vehicle speed sensor (installed in the speedometer) - informs the control unit about the vehicle speed;
- power steering switch and air conditioning switch (if installed) - inform the control unit about the inclusion of these systems so that the control unit can adjust the engine idle speed to compensate for the additional load on the engine from these systems;
- exhaust gas sensor (only on models with catalytic converter) - sends information to the control unit about the oxygen content in the exhaust gases.
The signals from all these sensors are analyzed by the electronic control unit. Based on this information, the electronic control unit regulates the operation of the fuel injectors (by changing the pulse duration - the period of time during which the injectors are open - in order to get a richer or leaner fuel mixture, depending on what is needed). The composition of the fuel mixture and the engine idle speed are constantly changed by the electronic control unit in order to provide optimal engine starting (cold or hot start), warming up the engine, idling the engine, the best engine performance when driving on the highway and during a sharp increase in speed.
The ECM also fully controls the idle speed of the engine through an additional air supply valve. This valve, which is mounted on the throttle body (models with 1.6 liter engine) or intake manifold (models with 2.0 liter engine), controls the opening of the air passage that passes the throttle valve. When the throttle is closed, the ECM controls the opening of a valve that regulates the amount of air passing through the throttle body passage and thus controls the idle speed of the engine.
On models with a 1.6 liter engine, the throttle body has a device that can independently increase the engine idle speed when the engine warms up. This function is controlled by a temperature valve. When the engine is cold, the wax capsule in the valve (valve installed in the throttle body) small, and the fast idle cam keeps the throttle slightly ajar. As the engine warms up, the wax capsule expands, pushing the valve plunger up, which in turn turns the fast idle cam into position.
On models with a 2.0 liter engine, the increase in idle speed is controlled by an air control valve, which consists of a bimetallic spring and a damper. When the engine is cold, a bimetal spring keeps the throttle open. Air passes through the valve, which increases the air flow into the intake manifold. When the engine is running, a voltage is applied to the bimetallic valve spring, which gradually increases its temperature. When the temperature rises, the bimetal spring deforms and closes the damper, cutting off the additional air supply to the engine.
All models also have a solenoid valve for increasing the engine idle speed, which is controlled by an electronic control unit, on the throttle body. The solenoid valve controls the opening of an air duct that passes the throttle and is used to increase engine speed when power steering systems or air conditioning are on.
Attention! On some models, the valve may be installed but will not function.
On models with a catalytic converter, the electronic control unit also controls the exhaust system and the fuel vapor control system, which are described in the corresponding chapter.
If the signals received by the electronic control unit from the sensors are out of range or do not agree with each other, the electronic control unit switches to a protected mode of operation. In this case, the electronic control unit ignores incorrect sensor signals and takes a certain setpoint as the sensor signal, which will allow the engine to work, albeit with less efficiency. If the electronic control unit enters the protected mode of operation, a warning light on the instrument panel lights up and the corresponding fault code is stored in the memory of the electronic control unit.
If the warning light comes on, contact a specialist as soon as possible. In the repair shop, a complete diagnosis of the engine management system can be carried out using electronic diagnostic equipment, which simply needs to be connected to the diagnostic socket.
Attention! The engine ECU also has a self-diagnosis mode that can be used by a car enthusiast. For more information see subsection 6.3.1.12.