Why does the engine vibrate when the car is idling?
3 Answers
Car idling vibration may be caused by the following reasons: 1. Dirty throttle valve: When the car is started, the engine is in an idling state, and air needs to continuously pass through the throttle valve into the cylinders to mix with gasoline for combustion. If the throttle valve is too dirty, it will reduce the air intake into the intake manifold. When this air intake fails to meet the normal air-fuel ratio, it will cause engine vibration. 2. Excessive carbon deposits inside the engine: When there is too much carbon buildup inside the engine, the gasoline sprayed by the cold start injector will be largely absorbed by the carbon deposits, resulting in an overly lean mixture during cold starts and making it difficult to start. 3. Faulty spark plugs or ignition coils: If spark plugs are not replaced for a long time, the electrode gap may become too large, affecting the ignition timing. This not only causes engine vibration but also increases fuel consumption. 4. Unstable oil pressure: It is recommended to visit a 4S shop to check the fuel supply pressure and the intake pressure sensor. If the fuel pump supply pressure is abnormal or the intake pressure sensor values are incorrect or malfunctioning, it can cause body vibration. In this case, check the oil pressure and replace components if necessary.
I've encountered this situation before, where the engine vibrates noticeably at idle, mainly due to combustion imbalance. For example, excessive carbon buildup in the engine can affect cylinder performance; aging spark plugs may fail to ignite properly; or the rubber in engine mounts deteriorates and loses its damping effect, turning what should be a vibration-absorbing component into a rigid one that transmits vibrations. These are idle-specific issues that tend to smooth out at highway speeds. If ignored, the vibrations will become more frequent, reducing driving comfort and potentially damaging other components like the drivetrain. Regular maintenance is recommended, such as checking spark plugs every 30,000 kilometers and cleaning throttle body carbon deposits. Don't wait until minor vibrations turn into major repairs—spending a few hundred dollars to replace mounts or clean the system can significantly reduce vibrations. Paying attention to idle noise during normal driving can help gauge the severity of the issue early on.
My car was shaking violently at idle last year, like a sieve. At that time, the fuel consumption also increased significantly. A veteran mechanic told me it was due to clogged fuel injectors causing uneven fuel spray and vibration, or possibly failing ignition coils where each ignition caused a shake. At idle, the engine runs slower, so these issues become more noticeable. The shaking made the car feel noisier and more irritating, especially when stuck in traffic waiting at red lights. Later, I went to a professional shop for cleaning and part replacements, and the symptoms disappeared. By the way, don’t always drive at low speeds—taking the car on the highway occasionally helps burn off carbon deposits. Checking is simple: plug a diagnostic tool into the OBD port to read fault codes—it’s cost-effective and reassuring, preventing further engine wear.
