Abnormal noise of n46 engine of cold car four-cylinder 3-series BMW.

One reason that can't be ignored is "carbon deposit", which will cause insufficient combustion of gasoline and make the engine shake and make abnormal noise. The influence of engine carbon deposition on automobiles is considerable. First, the engine power is reduced, that is, the power output is uneven and gradually decays, in other words, it is getting less and less powerful. The second is to increase fuel consumption and increase your economic burden. Third, it is difficult to start a cold start, that is, it is difficult to strike a fire and it is not easy to get a taxi. Finally, serious carbon deposition in the combustion chamber will also cause cylinder knocking, and low-speed acceleration will produce noise and damage the piston and crankshaft, thus seriously affecting the safety of the automobile. Then the discharge exceeds the standard, which not only fails the annual inspection, but also directly aggravates the harm of environmental pollution.

Another reason is that the throttle valve is out of order. The above two problems will cause engine jitter and unstable speed (Baidu Germany Marti, professional technician to solve the problem for you)