What should I do if the Jetta car idles unsteadily? Why does the Jetta idle unsteadily when it is co

Air intake system (1) Intake manifold or various valves leaking.

When the air that should not enter, gasoline vapor, and combustion exhaust gas enter the intake manifold, the mixture is too thick or too thin, and the engine burns abnormally. When the leakage position only affects individual cylinders, the engine will shake more violently, which will have a greater impact on the idle speed of the cold car. Common causes are:

loose intake manifold clamp or cracked hose; Air leakage from the intake manifold gasket; Damage to the intake manifold or other parts to grind out of the intake manifold; Injector O-ring leakage; The plug of the vacuum tube falls off and cracks; The crankcase forced ventilation (PCV) valve has a large opening; The activated carbon tank valve is normally open; Exhaust gas recirculation (EGR) valve is not closed tightly, etc.

2) Excessive fouling of the throttle and intake.

The excessive carbon and dirt deposits in the throttle valve and the surrounding air intake, and the change in the cross-sectional area of the air channel, make the control unit unable to accurately control the idle air intake, resulting in the mixture being too thick or too thin, and making the combustion abnormal. Common causes are: oil or carbon deposits on the throttle; There is oil and carbon deposits in the air intake tract around the throttle; Idle stepper motors, duty cycle solenoid valves, and rotary solenoid valves have oil stains and carbon deposits.

3) Failure of the idle air actuator.

Inaccurate idle air control due to a faulty idle air actuator. Common causes are: throttle motor damage or card issuance; Idle stepper motors, duty cycle solenoid valves, rotary solenoid valves are damaged or hairpinned.

4) Inaccurate air intake.

The control unit receives the wrong signal and sends out the wrong command, which causes the engine idle air intake to be inaccurate, so that the engine burns abnormally, which is an indirect cause of idle instability. Common causes are: air flow meter or its line failure; Failure of the inlet pressure sensor or its wiring; The plug of the engine control unit is in poor contact due to water ingress or internal computer failure.

Fuel system. 1) Injector failure.

The uneven amount of fuel injection and the mist of the injector cause an imbalance in the power emitted by each cylinder. Common causes are: clogged injectors, poor sealing, and linear fuel injection.

2) Fuel pressure failure.

If the oil pressure is too low, the atomization state of the fuel injected from the injector is poor or the fuel injected is linear, and only oil droplets are sprayed in serious cases, and the amount of fuel injected is reduced to make the mixture too thin; The oil pressure is too high, and the actual fuel injection volume increases, making the mixture too concentrated. Common causes are: clogged fuel filter; Fuel pump strainer clogged; The fuel pump's pumping capacity is insufficient; The spring elasticity of the fuel pump safety valve is too small; deformation of the inlet pipe; The fuel pressure regulator is faulty; The oil return line is deflated and blocked.

3) Inaccurate fuel injection.

The failure of each sensor or line causes the control unit to issue wrong instructions, so that the fuel injection volume is incorrect, resulting in the mixture being too thick or too thin, which is an indirect cause of unstable idling. The specific causes are: malfunction of the air flow meter (or intake manifold pressure sensor); Faulty throttle position sensor; throttle idle switch failure; Coolant temperature sensor failure; Faulty inlet air temperature sensor; Failure of the oxygen sensor; The lines of the above sensors have open circuits, short circuits, and ground faults; The plug of the engine control unit is in poor contact due to water ingress or internal computer failure.

Causes of unstable car idling.

1. Air leakage from the intake manifold.

When the air that should not be entered, gasoline vapor, and combustion exhaust gas enter the intake manifold, the mixture is too thick or too thin, causing the car to idle unsteadily.

2. Too much carbon deposition on the throttle.

Excessive carbon deposition in the throttle valve and surrounding air intakes, and changes in the cross-sectional area of the air channel, make it impossible for the control unit to accurately control the amount of air intake at idle, which will also lead to too thick or too thin mixture, resulting in unstable idling of the car.

3. Failure of the actuator of the air intake system.

There are many actuators in the engine intake system, such as throttle motors, idle stepper motors, duty cycle solenoid valves, air flow meters, intake pressure sensors, etc., which cause the car to idle unstable.

4. Fuel system failure.

Faults such as clogged injectors, clogged fuel filters, clogged fuel pump filters, faulty fuel pressure regulators, and clogged return pipes can all lead to incorrect fuel injection, resulting in over-concentrated or over-thin mixtures, resulting in unstable car idling.

5. Ignition system failure.

Faults such as ignition module failure, incorrect spark plug clearance, spark plug electrode ablation or damage, and excessive resistance of the high-voltage line lead to a decrease in ignition spark energy or misfire, resulting in unstable idling of the car.

The easiest way to eliminate it is to clean the throttle once, and if it doesn't work, you have to go to the repair shop to check.

Introduction:

1. The idle switch is not closed, diagnosis method: turn on the air conditioner and turn on the steering wheel when idling. The failure to increase the engine speed proves to be the fault.

Troubleshooting: Adjust, repair, or replace the throttle position sensor.

2. Idle control valve (ISC) failure, diagnosis method: check the actuation sound of the idle control valve, if there is no actuation sound, the idle control valve is faulty.

Troubleshooting: Clean or change the idle control valve, and use a special decoder to set the idle speed basically.

3. Air leakage in the intake pipeline, diagnosis method: If you hear the snorting sound of leakage in the air intake pipe, it proves that the air intake system is leaking. Troubleshooting: Find leaks, reseal or replace phase parts.

If the engine is unstable when the engine is running cold, it is easy to stall, but the idle operation is basically normal after the hot car, and the reasons are usually as follows:

1) When the car is cold, the additional air valve is not opened or the opening is too small, so that the idle speed of the engine is too low when the car is cold, resulting in unstable idling.

2) When the engine is cold, the idle control valve is faulty, and the opening is too small, so that the idle speed is too low when the engine is cold, resulting in unstable idling.

3) The water temperature sensor is faulty, so that the engine computer does not increase the idle speed and thicken the mixture according to the engine temperature when the car is cold, resulting in unstable idling.

4) The atomization of the injector is poor or partially blocked, which makes the quality of the mixture deteriorate or the amount of fuel injected is too small under the idle condition of the cold car, resulting in too thin the mixture and causing unstable idling.

Is it that the cold car is unstable in idling within two or three minutes after playing, floating up and down, as if it is about to turn off and pull up?