1, the spark plug is not working well; 2. The vacuum tube leaks; 3, high-voltage line leakage; 4. The 4.PCV valve is blocked; 5. The throttle position sensor is faulty; 6, stepper motor idling fault; 7, idle speed control valve failure; 8. Abnormal throttle opening; 9. Air leakage in the air intake system.

Second, what should I do if the idle speed is unstable?

Idle speed instability is characterized by engine jitter and uneven speed at idle speed. The reasons are: the idle air metering hole is blocked, the idle device is not working normally, the spark plugs of individual cylinders are too weak, the seals of individual valves are not tight, the intake manifold leaks air, the ignition time is too early or too late, and the idle speed is not adjusted properly. When the idle speed of the engine is unstable, the idle speed should be adjusted first. If the fault cannot be eliminated after idle speed adjustment, check whether the idle metering hole and idle air metering hole are blocked. If the metering hole is blocked, clean it with gasoline or acetone and blow it with compressed air. If the metering hole is not blocked, to stabilize the engine speed at a certain speed, you can observe whether the middle and lower gaskets of the intake manifold or carburetor are leaking. If there is air leakage, it can be eliminated by fastening screws or adding or subtracting gaskets. If the idle speed is unstable and the engine power decreases, the working condition of the spark plug, the sealing performance of the valve and the ignition time should be further checked, and maintenance and adjustment should be carried out if necessary.

Third, how to distinguish poor idle speed?

The normal working engine should be able to run evenly in the speed range of 300-500 rpm. If the lowest stable speed of the engine exceeds this speed range, or the engine flameout and unstable speed occur within this speed range, there is no idle speed or poor idle speed. When the idle speed is poor, it can be divided into idle flameout, unstable idle speed and excessive idle speed according to its fault characteristics. If the engine runs well from low speed to high speed after starting, but turns off immediately after releasing the accelerator pedal, or turns off after unstable operation, it belongs to idle flameout fault. If the engine is not running smoothly at idle speed, the exhaust pipe makes a "chug chug" sound, which is generally a fault of unstable idle speed. If the lowest stable speed of the engine is higher than the specified range, and the speed cannot be reduced, it is considered that the idle speed is too high or there is no idle speed fault.

Fourth, how to adjust the idle speed?

Idle speed adjustment must be carried out under normal conditions, such as normal engine temperature, proper valve clearance, normal ignition system, good sealing of all pipelines, full throttle opening and tight throttle closing. When adjusting, first loosen the throttle opening adjustment screw to make the engine reach the lowest stable speed. Then screw in the idle speed adjusting screw with a screwdriver, and then slowly unscrew the idle speed adjusting screw when the engine is about to stall, so that the engine can run smoothly and reach a high speed. Then loosen the throttle opening adjustment screw to make the engine speed as low as possible. Then adjust the idle adjustment screw to increase the engine speed. Repeat this process until the throttle opening is minimum and the engine runs at the lowest stable speed. Finally, increase the speed and suddenly close the throttle, so that the engine can still turn without stalling.

5. What should I do if I stall at idle speed?

When the engine turns off at idle speed, the idle speed should be adjusted according to the actual situation. After adjustment, if the fault disappears, it is improper adjustment of the idle screw. After adjustment, if the fault can't disappear, you can turn on the throttle and let the engine continue to run. Check the carburetor and intake manifold gasket for air leakage with cotton yarn or paper. If there is no air leakage, you can remove the idle metering hole for inspection, blow through the idle oil circuit at the same time, and then reassemble the test. If the fault disappears, the idle metering hole and idle oil circuit are blocked. For carburetor with idle stop valve, check whether the electromagnetic coil circuit of idle stop valve is normal. If the idle fuel-saving metering hole is blocked due to abnormal electromagnetic coil circuit, repair the idle stop valve.

6. What if the idle speed is too high?

When the idle speed of the engine is too high, start the engine first, and then control the throttle arm by hand to close the throttle. If the idle speed is normal at this time, it means that the throttle tension spring is too soft and should be replaced. If closing the throttle valve by hand is ineffective, check whether the throttle shaft is loose or whether the throttle valve is closed tightly. If the throttle valve is not tightly closed or the throttle shaft is loose, please repair it. If the throttle valve is normal, check whether there is slight air leakage under the throttle valve. If there is, eliminate the air leakage. If not, further adjust the idle speed until the idle speed is appropriate. ?