What Causes Car Engine Shaking During Startup?
2 Answers
Car engine shaking during startup is caused by: low ignition energy, carbon buildup on valves and intake passages, and improper air-fuel mixture. Low ignition energy: The first issue a car faces during cold starts is low temperature. The engine temperature is insufficient, and neither the fuel nor the lubricating oil has reached optimal temperature. Therefore, more fuel needs to be injected during cold starts to meet power requirements. The larger the spark plug gap, the lower the ignition energy. During low temperatures, fuel atomization is poor, requiring higher ignition energy. After prolonged use, the spark plug gap tends to widen, leading to reduced ignition energy, which affects performance and causes the car to shake.
Having driven for decades, I've found startup shaking usually stems from a few common issues. Either the spark plugs are severely carbon-fouled or the electrodes are excessively worn, causing unstable ignition that makes the engine shudder like it's gasping. Another culprit could be a throttle body clogged with sludge, disrupting the air-fuel mixture due to restricted airflow, triggering symptoms at startup. Engine mount rubber cushions aging and losing their firm grip can also make the whole vehicle shake noticeably, especially in older cars. A weak battery may exacerbate power supply issues, worsening the shaking. My advice: prioritize checking spark plugs and throttle body cleaning—basic fixes costing just tens of dollars can resolve core problems. Don't delay to avoid damaging other components. Regular maintenance is truly key; carbon deposit cleaning saves considerable hassle long-term.
