Sudden wobble or a thump? Slow down and pull over
A wobble that appears out of nowhere can be a loose wheel, a damaged tyre or a broken suspension part. Ease off without braking hard, pull over somewhere safe and switch off, then look at the tyres from the side away from traffic. Don't drive on a wheel you're not sure of. If anyone is hurt or in danger, call 111.
When does the car shake?
| Usual suspects | How urgent | |
|---|---|---|
| Parked, engine running | A misfire, worn engine mounts or a rough-running engine | Soon; stop if the engine light flashes |
| At one speed on the motorway, then fades | A wheel out of balance | Soon |
| Worse the faster you go | A damaged tyre, balance, or worn suspension | Soon; slow down meanwhile |
| Only when braking | Brake discs | This week |
| Pulling away, or turning under power | CV joints or engine mounts | Soon |
| Steering wiggles, car wanders | Worn steering or suspension parts | Soon |
Why is my car shaking at idle?
At idle the wheels aren't turning, so the shake is coming from the engine or the rubber mounts that hold it. The usual causes are a misfire (one cylinder not firing properly, often a spark plug, coil or injector), an air leak into the intake, or tired engine mounts letting normal engine movement through to the cabin.
A misfire will often bring on the engine light, and a flashing one means stop. AA New Zealand also lists an engine that runs very roughly or stalls among the signs of trouble with the engine computer. A code read is the place to start: our page on the check engine light covers what happens next.
Why does the car wiggle at motorway speed?
A wheel that's out of balance shakes the car and the steering wheel. Wikipedia's tyre balance entry says the disturbance generally grows with speed, and that it can seem worst around one speed, where the wheel spins at the same rate the suspension naturally bounces.
A pothole can knock a balance weight off or bend a rim. A tyre with a visible bulge in the sidewall is a different matter: put the spare on or get help, and don't carry on with it.
Clicks and shakes on the turn
A click-click-click on full lock in a car park, or a shake when you put your foot down, points to a CV joint (the joint that lets a front wheel steer and drive at once). AA New Zealand says a split CV boot lets the grease out, and replacing a cracked boot before the joint fails is the smaller job.
What to check once you've stopped safely
The tyres
Look for a bulge, a cut, or a tyre that sits lower than the others.
The wheels
If a wheel was off recently, ask whoever refitted it to check the nuts. Don't go far on a wheel you think is loose.
The dash
An engine light, steady or flashing, sends you to the engine side of things.
The pattern
Idle, one speed, braking or turning? Note it for the mechanic.
What the mechanic will check
For a shake on the move: tyres, wheel balance and rims, wheel bearings, steering joints and suspension bushes, then a road test. For a shake at idle: the stored engine codes, misfire counts, plugs and coils, and the engine mounts.
A good mechanic tells you what they found, not just what they replaced. Ask for that in writing with the quote.
Will a shaking car fail a WoF?
Tyre condition, steering and suspension are all on the WoF list, and the MTA says steering and suspension must be safe and secure. A shake from a worn suspension part or a damaged tyre is the kind of thing an inspector looks for. An idle shake from the engine is different, because the MTA says engine condition isn't part of the inspection.
What you can do, and what to leave
You can
- Check tyre pressures on a cold car, using the figures on the inside door frame.
- Look over the tyres for bulges, cuts and uneven wear.
- Note when the shake happens and whether a light is on.
Leave to the mechanic
- Balancing wheels and checking rims.
- Suspension, steering and CV joint checks on a hoist.
- Engine codes, misfire tests and engine mounts.
Where we'd start
We'd note exactly when it shakes and put that in the note, because a mechanic who knows whether to start at the wheels or the engine saves time. If the shake came on suddenly, we wouldn't go another kilometre until a look at the tyres from the roadside rules out a loose wheel or a bulge.