Why Does the Engine Shake When Starting?
2 Answers
The most common reason for engine shaking during startup is a dirty throttle body or excessive carbon buildup in the fuel injectors. Below is a detailed explanation of the causes of engine shaking during startup: 1. Excessive carbon deposits: When there is too much carbon buildup inside the engine, the gasoline sprayed by the cold-start injector is largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture during cold starts, making it difficult to start. After starting, the gasoline adsorbed on the carbon deposits is sucked into the combustion chamber by the engine's vacuum, enriching the air-fuel mixture. This fluctuation between lean and rich mixtures causes idle shaking after a cold start. 2. Abnormal coolant temperature: The engine operates within a specific temperature range. High coolant temperature can lead to advanced ignition timing, disrupted air-fuel mixture ratios, thinning of engine oil viscosity, and reduced lubrication performance. 3. Clogged fuel injectors: Impurities in gasoline can clog the injector nozzles, causing inconsistent fuel spray volumes among injectors. This results in uneven cylinder operation frequencies, leading to engine shaking. 4. Low cylinder pressure: Engines come in configurations such as 3-cylinder, 4-cylinder, 5-cylinder, 6-cylinder, and 8-cylinder. When one cylinder malfunctions, a misfire occurs, causing the engine to shake.
My car occasionally shakes violently when starting, especially on cold winter mornings. It feels like the entire cabin is vibrating. The most common causes are worn-out spark plugs or excessive carbon buildup, preventing complete fuel combustion and leading to uneven cylinder operation. Additionally, if the engine mounts are loose or cracked, the transmitted vibrations become more noticeable. I've also observed that when the battery voltage is low during startup, the electrical equipment struggles to function, exacerbating the shaking. Regular maintenance checks on the ignition system, replacing spark plugs, or cleaning the throttle body usually resolve the issue. Prolonged neglect can increase wear and affect the engine's lifespan, making repairs more costly.
