Why does my car shake or vibrate when it is stationary?

An engine at idle is doing the hardest version of its job: producing just enough power to keep itself turning, with almost no flywheel effect to smooth it out. Everything that is slightly wrong shows up here first, which is why idle quality is such a good early diagnostic. Fortunately it is also one of the few faults an owner can meaningfully narrow down without any tools, because the tests are all about changing the load on the engine and noticing what the shake does.

Safety

Step by step

1. Describe the shake accurately first.A smooth tremor at a constant frequency feels different from an uneven stumble with a rhythm to it. Note where you feel it — the seat, the steering wheel, the pedals, the mirrors — and whether it is worse cold, worse hot, or the same throughout. That description is most of the diagnosis.
2. Do the gear test on an automatic.With the handbrake firmly on and your foot on the brake, move from park to drive. If the vibration appears or noticeably worsens, the engine's movement is being transmitted into the body, which points at worn engine or gearbox mountings. If it is the same in both, look at how the engine is running.
3. Do the equivalent test on a manual.In neutral with the clutch up, note the idle. Then switch on the air conditioning and the rear screen heater, which loads the engine. A shake that appears only under that extra load points at an engine struggling to hold idle, or at mountings passing the extra movement through.
4. Check whether it is worse cold or hot.Rough only for the first minute or two from cold, then fine, is a common pattern for a slightly worn engine, a cold-start enrichment issue or, on a diesel, glow plugs. Rough only once hot points more towards a sensor drifting out of range or a fuelling problem that appears as things expand.
5. Look for a misfire pattern.A misfire feels like an uneven beat rather than a constant buzz — the engine stumbles and catches, sometimes with a slight rocking. Modern cars usually flag it with an engine management light, which may flash under load. A flashing engine light is a specific warning that unburnt fuel is reaching the catalytic converter, and that means stop driving and get it diagnosed.
6. Consider an air leak.A split or disconnected hose after the air-flow measurement point lets in air the engine control unit did not count, which makes the mixture wrong and the idle unstable. It is a common and relatively cheap fault, and it often produces an idle that hunts up and down rather than simply shaking.
7. Understand engine mountings.The engine and gearbox sit on rubber or fluid-filled mountings that let them move without transmitting vibration into the body. Rubber perishes and fluid mountings leak, and when one fails, normal engine vibration that used to be absorbed is passed straight into the cabin. It usually creeps up over years, gets worse in gear or with the air conditioning on, and is often accompanied by a clunk when pulling away or changing gear.
8. Do not overlook the boring causes.A very low battery on a stop-start car, a heavily loaded air conditioning compressor on a hot day, a diesel in a particulate filter regeneration cycle, or simply a car that is overdue a service. Regeneration in particular changes idle speed and note noticeably, and is completely normal.
9. Get the codes read before replacing anything.A misfire code identifies the cylinder, which turns a vague problem into a specific one. Ignition coils, plugs, injectors and compression all produce misfires and they cost very different amounts, so the code is worth having before the conversation about parts.
10. Separate this from vibration while moving.A shake that only appears at road speed, or only through the steering wheel above a certain speed, is a wheel and tyre problem rather than an engine one, and it is a different diagnosis entirely. A vibration under acceleration but not at idle is different again.

Tips

• Film the rev counter at idle for thirty seconds. A needle that dips and recovers rhythmically tells a garage far more than a description, and it distinguishes a misfire from a hunting idle immediately.
• Note whether the vibration is present with the engine idling and the car switched to neutral while stationary at lights. That single observation rules mountings in or out on most automatics.
• If the shake arrived at the same time as a service, mention it. A loose air hose or an incorrectly seated component after work is common and quickly resolved.

Common mistakes

• Continuing to drive with a flashing engine management light — A flashing light generally indicates a misfire severe enough to damage the catalytic converter. That is a much larger bill than the misfire, and it accumulates by the mile.
• Replacing all the ignition parts on a guess — A misfire code names the cylinder. Replacing plugs and coils across the engine without reading it is expensive and often misses an injector or a compression problem.
• Assuming any vibration is engine mountings — Mountings usually get worse over years and change with gear selection. A vibration that appeared this week is far more likely to be how the engine is running.

If it doesn't work

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