Why does the engine shake when starting?

[HazelAnn]

The reason the engine shakes when starting is due to a dirty throttle body or excessive carbon deposits on the fuel injectors. When there is too much carbon buildup inside the engine, the gasoline sprayed by the cold-start injector can be largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture during cold starts. This makes starting difficult and causes the engine to idle roughly after a cold start. Solution: Clean the fuel system, check if the idle control valve has carbon buildup and clean it if necessary, or drive at low gear with high engine speed for a period of time to increase the engine's air intake and fuel flow, which helps remove carbon deposits from the injectors. Carbon buildup inside the engine is unavoidable, so car owners must regularly clean and inspect it.