Why does the car vibrate when idling, but the vibration lessens when driving?

When a car vibrates whilst idling but the vibration subsides whilst driving, the cause is usually an uneven engine run or worn engine mountings. Whilst driving, the revs are higher and the engine is under load, so a minor running problem or a worn engine mount is not felt in the cabin in quite the same way. Here in Kirkkonummi, we identify the cause of the vibration by asking when it occurs: when the engine is cold, with the air conditioning on, or when the engine is warm. These three observations alone quickly narrow down the fault.

The car shakes when idling in cold weather: is the engine running unevenly or is a fastening loose?

If the vibration is at its worst immediately after starting and subsides as the engine warms up, check the engine’s running condition first. A cold engine runs on a richer mixture and at a higher idle speed, which is when faults are most evident. The cause may be worn spark plugs, a weak ignition coil, a dirty injector or an intake air leak. In such cases, one cylinder will run poorly and the engine will produce uneven knocks, which can be felt in the seat and on the steering wheel. We cover this topic in more detail in the article ignition problems and jerking in a petrol car.

If the vibration is only noticeable once the engine has warmed up, you should check the mountings. Rubber or fluid-filled mounts support the engine and dampen its vibrations. When the rubber cracks or compresses, or when a fluid-filled mount leaks, the vibration is transmitted directly to the bodywork. At idle, the revs are low and the vibration is strong. When driving, the revs increase, the frequency of the vibration changes, and the vibration is dampened or disappears completely.

When vibrations subside whilst driving, the cause is often a fault in the engine’s running or a worn engine mount.

Vibration when idling with the air conditioning or gear engaged: how to pinpoint the cause

Try this whilst the car is parked and the brake is fully applied: switch the air conditioning off and on, with the gearbox in neutral and then in gear. The air conditioning compressor places a load on the engine, but the idle speed should remain steady. If the vibration only increases when the compressor engages, the cause may be an issue with the idle speed control, a weak engine or the compressor’s belt drive. We’ll check this air conditioning the operation and condition of the belt, so that you know whether the fault lies with the air conditioning or the engine.

Engaging the gearbox transfers the load from the drivetrain to the mountings. The engine tends to rotate around its axis, and a loose mounting allows this movement. If vibration and a slight thud occur only in the ‘D’ position or when changing gears, the support cushions are the likely cause. In a diesel car, idling vibration and rattling can also be caused by the dual-mass flywheel. The cause can only be definitively identified by inspecting the car whilst it is raised.

If your car shakes whilst idling, make a note of these observations before taking it to a garage

Make a note of when the vibration starts: during a cold start, when the engine is warm, with the air conditioning on, or when a gear is engaged. Also note whether the engine warning light comes on and whether fuel consumption has increased. This information speeds up the fault-finding process, as we know where to start. We’ll investigate the vibration in diagnostics by reading the fault codes and operating data. A fault code on its own is not enough, so we also check the engine and gearbox mountings.

Severe vibration, a flashing warning light or a drop in power require immediate investigation, as the fault may worsen. A loose mount also puts strain on the hoses, exhaust pipe and other fixings. We service all car makes in Kirkkonummi, Siuntio, Espoo and Veikkola. Call us on 045 896 0556 on weekdays between 8 am and 5 pm and let us know when the vibration occurs, so we can arrange the next steps.