汽车怠速（Car idling）.docVIP

汽车怠速（Car idling） The unstable idling of engine is one of the common faults in automobile. Although most cars now have faulty self diagnostic systems, there may be a car malfunction, while the self diagnostic system shows normal fault codes or shows no code related to the malfunction. This is usually caused by an actuator malfunction or a conventional mechanical fault that is not directly controlled by an electronically controlled unit (ECU). Listed below are the common causes of engine idling instability and its diagnosis and troubleshooting methods. 1 、 idle switch is not closed When the idle contact is broken, the ECU determines that the engine is in a state of partial load. At this time, the ECU determines the injection amount and injection time according to the air flow sensor and the crankshaft position and the speed signal. But at this time, the engine is working in idle conditions, less intake, resulting in excessive gas mixture, speed rise. When ECU received mixed oxygen sensor feedback signal to reduce the gas concentration, injection volume, increase the opening of the idle speed control valve, causing the mixture too thin, the speed decreased; when the ECU receives a mixed gas oxygen sensor feedback signal, and increasing the amount of fuel, reducing the opening idle control valve. And causing the mixture too thick, up to speed. So repeated, so that the engine idling instability. In idle conditions, turn on the air conditioner, turn the steering wheel, and the light will increase the load of the engine. In order to prevent the engine from stalling due to the increase of load, the ECU will increase the fuel supply to maintain the balanced operation of the engine. The idle speed contact is broken, ECU thinks that the engine is not in idle condition, it will not increase the fuel supply, so the speed is not improved. Diagnosis method: when idle, turn on the air conditioner and turn the steering wheel. If the engine idle speed is not increased, then the idle