What is the reason why the engine pointer is idling a little?

This is 1 engine jitter caused by unstable idle speed, spark plugs and cylinder lines. The larger the gap between the anode and cathode of the spark plug, the smaller the surface area of the ignition point, which leads to the reduction of ignition energy required to compress the oil-gas mixture, which leads to the decrease of power, thus affecting the power and making the automobile engine shake. In addition, the aging of the ignition coil may lead to poor flow or leakage of high-voltage electricity, and may also lead to unstable idle speed of the engine and jitter due to power reduction. 2. Engine jitter caused by fuel-air mixture ratio is a common phenomenon in old carburetor cars, but it will also happen if there is something wrong with the computer in EFI cars. The reason is simple and easy to understand. I learned the working principle of internal combustion engine in junior high school, so I don't want to go into details here. It is worth mentioning that the oxygen sensor is installed near the root of the engine exhaust pipe in the current EFI vehicle, which is an important parameter for the driving computer to control fuel injection. In closed-loop controlled vehicles, the minimum working temperature of the oxygen sensor is 370 degrees Celsius. If the temperature in the exhaust pipe is lower than 370 degrees Celsius just after the vehicle is started, the oxygen sensor will not work, which will cause a temporary judgment error of the driving computer, resulting in an error in the control of oil-gas mixing and ignition time through the actuator. 3. The carbon deposit on the valve, throttle and idle valve leads to jitter. Most of today's family cars are equipped with high-speed engines. When this kind of engine needs to shift gears, the engine speed should be 2500 rpm, otherwise it is easy to cause carbon in all areas of the engine. If there is carbon deposit on the valve of the engine and the valve seal is not tight, it will lead to the wrong judgment of the driving computer and affect the oil-gas mixture ratio (air is greater than the normal ratio). Too much carbon deposit can also cause the phenomenon of carbon deposit absorbing gasoline, just like the principle of soil absorbing water is similar, which leads to less gasoline than normal, insufficient power and engine jitter. As we all know, the common engines are composed of three or more cylinders. After long-term use, the ignition gap and time control of spark plug will be different, but the driving computer can't diagnose such a small deviation and still treat it equally, which leads to errors in practice and theory. Therefore, some cylinders generate less power, resulting in engine jitter. In addition, after the engine is used for a long time, the wear degree of each cylinder liner and piston is different, which leads to the gap between the cylinder plug ring and the cylinder wall being larger or smaller, especially during cold start, when there is no oil lubrication, the cylinder with large gap will lose part of the high temperature atmosphere, thus reducing the power output and leading to engine jitter. 5. The water temperature sensor is also an important basis for the driving computer to judge the running state of the engine at that time. The amount of fuel injected by the fuel injection system is directly controlled by the water temperature inside the vehicle. For example, if the temperature of the engine during cold start is-10 degrees Celsius, but the sensor "tells" the computer that the current temperature is 20 degrees Celsius, then the computer will inject fuel at 20 degrees Celsius, and the fuel injection amount will naturally be less, and the power shortage will naturally appear, so the engine will shake. 6, other factors lead to jitter In addition, dirty idle valve body, poor engine oil, abnormal operation of idle motor and other reasons may cause the phenomenon of unstable idle speed of vehicles.