The engine screeched. What happened?

This situation can be divided into two phenomena, one is the timing of engine shift, that is, the sound of engine vibration caused by premature shift. The other is the fluctuation of engine idle speed, that is, the noise caused by too dirty throttle and too high engine speed when collecting oil. If it is the shift timing, I suggest you change the shift timing. The so-called optimal shift timing is actually to make the engine run in this optimal speed range as much as possible, and this range is often manifested in the technical parameters near the speed range where the maximum torque appears.

This compromise value is not exactly the same for different engines, so the shift timing is not exactly the same. It is not necessarily scientific to look at the speed of maximum torque completely. Although some engines have high maximum torque speed, they often have enough torque output (above 90%) from 2500 rpm. At this time, there is no need to shift gears at that speed dogmatically. It can also be based on the feeling of actual operation. If the engine feels stuffy after shifting gears, it must be early. The car after shifting is still full of momentum, and the lowest speed that can achieve this effect is the best shifting speed of the whole car. Secondly, if the throttle is carbon-deposited, it is recommended to go to a maintenance franchise store and clean it before matching it.