What is the reason for engine shaking at idle but not when accelerating?

[MacRuth]

The reasons for engine shaking at idle but not when accelerating are: 1. Changes in fuel injection volume; 2. Malfunction in the fuel pump pressure regulator or sensors causing faulty fuel injection correction signals; 3. Cracked vacuum booster pipe; 4. Carbon buildup or dirt on the throttle body, or incorrect positioning of the throttle position sensor. The connection points between the engine and the frame are equipped with engine mounts, which absorb vibrations generated during engine operation. An engine is a machine that converts other forms of energy into mechanical energy, including internal combustion engines, external combustion engines, electric motors, etc. Idling results in low engine speed, which can propel the vehicle forward under light load conditions.

[CarterMarie]

I think this is a pretty common issue, and the most likely cause is carbon buildup in the engine. At idle, the engine runs at low RPM with minimal air flow. If the throttle body or idle air control valve gets carbon deposits, it can cause uneven air intake, leading to severe shaking. But when you step on the gas, the increased RPM and air flow can blast through the carbon buildup, making the shaking disappear. I remember last time I had this issue—cleaning the throttle body didn’t cost much and fixed it right away. If you often drive short distances or at low RPM, carbon tends to accumulate faster. I’d recommend an engine cleaning every 10,000 km or so. Don’t ignore this—it could lead to more serious problems, like affecting the ignition system and fuel efficiency. Fixing it early keeps your ride smooth and your mood better.

[StEleanor]

If the engine shakes at idle but stops when you step on the gas, it's most likely an issue with the ignition system. When spark plugs or ignition coils age slightly, they may produce uneven sparks at low RPM, causing the car to shake. However, at higher RPMs, the increased spark frequency makes the issue less noticeable. From my experience, check the spark plugs—see if they're too carbon-fouled or have reached the end of their lifespan and need replacement. Spark plugs should be replaced every few tens of thousands of kilometers—it's cheap and easy. Additionally, unstable idle can also affect emission levels, potentially causing your car to fail environmental inspections, which is a hassle. I often handle this myself as preventive maintenance; regular upkeep can significantly reduce the risk. Overall, this kind of issue isn’t too serious, but addressing it promptly can protect the engine and extend its lifespan, making the drive smoother and more enjoyable.

[Ulysses]

This issue is usually caused by worn engine mounts. At idle, the engine vibrates less, but if the mount is broken and can't hold it in place, the shaking becomes obvious. When you step on the gas, the higher RPMs stabilize the engine, reducing the vibration. I've encountered this before—just replacing the mount solved the problem without costing much. Engine mounts age quickly, so be cautious as other components might be affected. Drive smoothly, avoiding sudden braking or acceleration, to slow down wear. It's recommended to inspect and repair promptly to ensure safety.

[AthenaMarie]

I think this issue might be related to sensors, such as a dirty mass airflow sensor. At idle, the sensor misjudges the airflow, causing uneven engine operation, but when accelerating, the parameters automatically adjust and the shaking disappears. Cleaning the sensor is cost-effective with good results and also extends the lifespan of related components. Ignoring unstable idle could lead to weak acceleration or even stalling, which would be dangerous. Pay attention to your vehicle's condition during daily use; early inspection leads to peace of mind.