What is the hissing sound of air leakage when idling?

The engine of Pacific car network hissed and leaked. Generally, after hearing this sound, the engine will lose power quickly. The possible reason is that the engine is overheated and the cooling system needs to be checked. Or the exhaust system is blocked and the vacuum tube leaks. When the engine is running, if you hear a "hiss" sound at the air filter at the intake of the carburetor, it means that the intake valve is leaking. A creaking sound heard at the exhaust pipe and muffler indicates that the exhaust valve is leaking.

What does it mean that the car is idling? I have been introducing car models recently. However, the problem of car idling is believed to be a relatively unfamiliar problem for novices. Many car owners have heard of the word "idling" and know that idling is not good, but the specific harm is not clear. What does idle speed mean? What harm does idling do to cars? Let's look at the hiss when the car is idling.

Causes of unstable idle speed

1. Intake system

(1) Air, gasoline vapor and combustion waste gas that should not enter the intake manifold or various valves leak into the intake manifold, causing the mixture to be too rich or too lean, which makes the engine burn abnormally. When the air leakage position only affects individual cylinders, the engine will shake violently, which has a great influence on the idle speed of cold cars. Common causes are: loose clamp of intake manifold or broken hose; Air leakage of intake manifold gasket; The intake manifold is damaged or other parts grind holes in the intake manifold; O-ring of fuel injector leaks; Vacuum tube plug falls off and breaks; The positive crankcase ventilation (PCV) valve has a large opening; The valve of activated carbon tank is normally open; Exhaust gas recirculation (EGR) valve is not closed correctly.

(2) Too much dirt on the throttle and air inlet; Too much carbon and dirt on the throttle and the surrounding air intake; Moreover, the cross-sectional area of the air duct changes, which makes the control unit unable to accurately control the idle air intake, resulting in the mixture being too rich or too thin and abnormal combustion. Common reasons are: the throttle has oil pollution or carbon deposition; There are oil stains and carbon deposits at the air inlet around the throttle; Idle stepper motor, duty solenoid valve and rotary solenoid valve are polluted by oil and carbon.

(3) Idle air actuator failure Idle air actuator failure leads to inaccurate idle air control. Common reasons are: the throttle motor is damaged or the card is issued; Idle stepper motor, duty solenoid valve and rotary solenoid valve are damaged or stuck.

(4) Incorrect air intake control unit receives an error signal and sends an error command, which leads to the engine's intake misalignment at idle speed and makes the engine burn abnormally, which is the indirect cause of unstable idle speed. Common causes are: air flowmeter or its line failure; Intake pressure sensor or its line fault; The plug of the engine control unit is due to poor water contact or internal computer failure.

What does it mean that the car is idling?

2. Fuel system

(1) Faulty fuel injector The fuel injection quantity of the fuel injector is uneven, and the fog is not good, resulting in uneven output of each cylinder. The common reasons are: the injector is blocked, the sealing performance is poor, and the ejected fuel is linear.

(2) Fuel pressure fault The oil pressure is too low, the fuel sprayed by the injector is in poor atomization state or the sprayed fuel is linear. In severe cases, only oil droplets are injected, the fuel injection quantity is reduced, and the mixture is too thin; When the oil pressure is too high, the actual fuel injection increases, making the mixture too rich.

(Photo/Text/Photo: Pacific Auto Network Q&A called Beast)