What is the cause of engine idling jitter when the car is cold?

After entering the vehicle factory for maintenance, the owner reported that the idling sloshing was obvious when the engine cooled down, and the sloshing gradually disappeared with the increase of engine temperature. Why does the engine idle only when the car is cold, and the shaking will disappear after the temperature rises? In the process of troubleshooting, the maintenance personnel connected the scan tool to detect the misfire of engine cylinder 2, and the number of times was more. Remove the double-cylinder spark plug and check that there is no abnormality in appearance. If the spark plug is replaced by another cylinder, the engine will shake after cooling. At this time, the engine data will be read, and the cylinder that is on fire is still two cylinders. When the two-cylinder spark plug is removed again, the spark plug smells of liquid and gasoline. It shows that the cause of the fire is probably not the fuel injector and spark plug. Measure the cylinder pressure and the data is normal. Restart the engine and see that there are a few bubbles in the coolant tank, and the coolant level is lower than the standard value. It is suspected that the cylinder combustion chamber is connected with the cooling water channel. Ask the boss if the cylinder gasket was changed not long ago. Remove the cylinder head, check the cylinder gasket, and find that the cylinder gasket is the product of the deputy factory. Because the thickness near cylinder 2 is thinner than other positions, the sealing performance of cylinder gasket becomes worse when the car is cold, and some coolant enters cylinder 2, which will not ignite the mixed gas in the cylinder. After the engine heats up, the cylinder gasket expands, the sealing effect returns to normal, and the engine is no longer on fire. After replacing the cylinder liner, start the trial operation, and the engine is normal in cold and hot state, and troubleshoot. In the case of a cold car, which is another reason why the cold car bumps and the hot car is normal, the mixture is not easy to catch fire, so it is necessary to add rich oil. Therefore, if the engine fuel filter is overloaded and blocked, or the fuel supply is insufficient, the operation of the engine cooler will become unstable. On the other hand, when the engine temperature rises and the mixture is easy to catch fire, the engine will resume stable operation and no longer shake. If the piston ring with the wrong size is used in the engine overhaul, if the size of the piston ring is smaller than the reference value when the engine is in the cooling state, the air tightness will be affected, which will lead to fire and fuzzy engine operation. After the engine is warmed up, the piston ring is heated and expanded, and the expanded piston ring fills the gap between the cylinder wall and the piston to restore air tightness and prevent the engine from shaking. Another cause of failure is abnormal signal of water temperature sensor. In the cold state, the water temperature sensor provides a signal that the water temperature is normal (90), and the engine control unit does not issue an instruction to enrich the fuel. At this time, in the engine with low temperature, the rich mixture can't be obtained, which makes the engine difficult to start and unstable, but when the engine temperature rises, the fault will gradually disappear. In order to ensure the normal operation of the engine, please use pure parts in engine repair and maintenance. Mahler provides filters, thermal management and engine parts for automobile after-sales service, and its performance fully meets the technical requirements of the factory.