What Causes Engine Idle Shaking During Cold Start?
2 Answers
Engine idle shaking during cold start can be attributed to the following reasons: Excessive Carbon Deposits: When there is excessive carbon buildup on the throttle body, fuel injectors, or intake manifold, or when there is too much carbon inside the engine, the gasoline sprayed by the cold start injector will be largely absorbed by the carbon deposits. This results in an overly lean air-fuel mixture during cold starts, causing the engine to shake. Low Cylinder Pressure: After prolonged engine use, the clearance between each cylinder liner and piston may become inconsistent. During a cold start, without proper lubrication from engine oil, cylinders with larger clearances may leak a certain amount of high-temperature gas through the gaps. This reduces power output, leading to low oil pressure and cylinder pressure, which results in insufficient power and engine shaking. Faulty Ignition Coil: If the ignition coil malfunctions, such as cracking and leaking electricity, it can cause insufficient or lack of spark plug ignition capability. Consequently, the air-fuel mixture in that cylinder will not combust properly, leading to engine misfire, difficulty starting, and acceleration shaking.
When the engine idles roughly during a cold start, it's usually due to some issues with the ignition system, such as unstable ignition caused by aging or carbon-fouled spark plugs. My car used to have this problem—it shook so badly that the steering wheel wobbled, but it was fixed after replacing the spark plugs. Another possible cause is a dirty throttle body affecting airflow; if air can't get in, the engine struggles to breathe. Insufficient fuel supply from the fuel pump is also a common issue, especially in cold temperatures when gasoline flow is poor—it's best to check the fuel system during seasonal transitions. If the shaking is severe, it might indicate a misfiring cylinder (where one cylinder isn't working), requiring an OBD scanner to read the trouble codes. Don’t overlook minor details like worn engine mounts failing to absorb vibrations. Get it checked at a repair shop early to avoid bigger problems like increased fuel consumption or hard starts. I recommend paying attention to these areas during regular maintenance to keep the engine running smoothly.
