What causes engine shaking during startup?
2 Answers
Engine shaking during startup is generally caused by severe engine carbon deposits, issues with the ignition system, unstable oil pressure, aging engine components, or excessive carbon buildup. The most common reasons for car shaking are a dirty throttle body or excessive carbon deposits in the fuel injectors. Below are relevant details: When there is excessive carbon buildup inside the engine, the gasoline sprayed by the cold-start fuel injector is largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture during cold starts and making it difficult to start. In this situation, the engine will only start easily once the carbon deposits have absorbed enough gasoline to reach saturation. After starting, the gasoline adsorbed on the carbon deposits is then drawn into the cylinders by the engine's vacuum suction and burned, making the air-fuel mixture too rich. This fluctuation between lean and rich mixtures causes idle shaking after a cold start. The lower the temperature, the more fuel is required for a cold start, and the presence of carbon deposits significantly affects whether the cold start proceeds smoothly. 1. Abnormal coolant temperature: The engine operates within a specific temperature range. If the coolant temperature is too high, it can lead to premature ignition timing, changes in the air-fuel ratio, thinning of the engine oil, and reduced lubrication performance. Common causes of shaking include low coolant levels, a stuck thermostat, a non-functioning fan, or an inaccurate temperature control switch. Resolving these issues will eliminate the shaking. 2. Clogged fuel injectors: The fuel injectors in electronic fuel injection vehicles are critical components for fuel delivery and have a long lifespan, often lasting hundreds of thousands of kilometers. However, the presence of gums in gasoline can clog the injector nozzles, causing uneven fuel delivery among the injectors. This results in inconsistent cylinder performance and engine shaking. The solution is to remove and clean the injectors. 3. Low cylinder pressure: Engines come in 3-cylinder, 4-cylinder, 5-cylinder, 6-cylinder, and 8-cylinder configurations. If one cylinder is not functioning properly, it can lead to a misfire and engine shaking. This is most noticeable in 3-cylinder engines, followed by 4-cylinder engines. A cylinder compression test can be performed using a compression gauge to check cylinder pressure.
Car engine shaking during startup is quite common, and I've experienced it several times myself. For example, last week, my car shook violently when starting, and I almost thought it was going to break down on the road. The main causes include carbon buildup or aging of the spark plugs leading to uneven ignition, clogged fuel injectors causing irregular fuel supply, a dirty air filter preventing sufficient air intake, or throttle body contamination affecting the air-fuel mixture. If it's a cold start in winter, the shaking can be more noticeable because the thickened engine oil increases friction between engine components. I usually do a quick check myself, like pulling out the spark plugs to see if they're blackened or listening to the engine sound during startup—if there's a clicking noise, it might indicate a weak battery. However, it's best to take it to a repair shop for a diagnostic scan rather than delaying it, as prolonged shaking can wear out engine mounts or sensors, leading to costly and dangerous issues. Regular oil changes and maintenance can prevent this problem—after all, safety comes first.
