A Volkswagen Baltic manual car. The car is difficult to start, and the engine starts to shake badly after starting. According to the experience, it looks like the engine is missing the cylinder. Test cylinder pressure, found that the pressure of a cylinder is below the standard value. Observe the cylinder valves with a car endoscope and find the intake and exhaust valves of the cylinder, especially the carbon intake and the gum on the intake valve. It is because of the serious carbon deposition of individual cylinders and the lack of strict valve sealing that the combustion of individual cylinders is not enough, resulting in engine failure. Because the car's carbon deposition and gelation is very serious, it can't be completely removed by using no demolition and washing, so it is decided to remove the cylinder head and remove carbon deposition. After carbon removal and reassembly, the engine is started (cold vehicle condition), the engine starts smoothly, and no longer jitter, and the failure phenomenon vanishes. After the incident, the car only ran in the last year and a half, and basically used only for going to and from work, seldom running high speed.