Severe engine shaking in reverse but normal in forward gear is caused by severe carbon buildup. Severe Engine Carbon Buildup: The most common cause of engine shaking due to severe carbon buildup is a dirty throttle body or excessive carbon deposits in the fuel injectors. When there's excessive carbon buildup inside the engine, the gasoline sprayed by the injectors during cold starts gets largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture that makes starting difficult. In this situation, the engine only starts easily after the carbon deposits become saturated with gasoline. Once started, the gasoline adsorbed on the carbon deposits gets drawn into the combustion chamber by the engine's vacuum, making the mixture too rich. This alternation between lean and rich air-fuel mixtures causes idle shaking after cold starts. Additionally, lower temperatures require more fuel for cold starts, making carbon deposits more likely to interfere with successful cold starts. The solution is to clean the fuel system and check if the idle air control valve has carbon deposits that need cleaning. Engine: An engine is a machine that converts other forms of energy into mechanical energy, including internal combustion engines (reciprocating piston engines), external combustion engines (Stirling engines, steam engines, etc.), jet engines, electric motors, etc. For example, internal combustion engines typically convert chemical energy into mechanical energy. The term engine can refer to either the power generation device or the entire machine including the power unit (e.g., gasoline engines, aircraft engines). Engines first originated in England, so the concept of an engine also comes from English, with its original meaning referring to "a mechanical device that generates power."
