While the engine runs
Car jerks when accelerating: causes and what to do
Jerking under acceleration usually means the engine is not burning well in every cylinder or is not getting the air or fuel it asks for. Spark plugs, coils, injectors, the air-flow meter or the turbo are the usual suspects, and on automatic cars the gearbox too.
See a garage soonWhile the engine runs
Reviewed by Daniel Morales, founder of Reprorace SL, on
Is it serious? Can I keep driving?
Carefully, and only as far as the garage. You can drive gently to the garage if the jerks are mild and there are no warning lights. If the engine light flashes, the car loses a lot of power or you smell burning, stop as soon as it is safe.
A careful, general answer: only someone who inspects the car can say whether it is safe to drive. When in doubt, stop somewhere safe and call for assistance.
Most likely causes
- Misfires: worn spark plugs or a failing coil, especially under load or uphill.
- Injectors: dirty or leaking, they meter fuel badly and the engine loses power in bursts.
- Air-flow meter or air leaks: a false air reading upsets the mixture.
- Fuel supply: a clogged filter or a weak pump cannot keep up under hard acceleration.
- Turbo or EGR: on diesels, a loose turbo hose or an EGR valve that does not close cause jerks and smoke.
Listed from more to less common in general; on your car they may be different. A fault-code reading and a check at the garage confirm which one it is.
To understand it better: What are engine misfires (P0300)? What is a mass airflow sensor and what symptoms does it cause when it fails? How does a turbocharger work and what does P0299 mean?
Car system: Ignition
What you can check yourself
Note when it happens: cold or hot, at what engine speed, with the tank nearly empty.
Check whether any warning light comes on, even briefly.
With the engine cold, look for loose or split hoses between the air filter and the engine.
Read the fault codes, pending ones included, even with no warning light.
Safe checks only: with the engine off and cold whenever you look under the hood, without taking anything apart and without touching hot or moving parts.
Related fault codes
- P0300Random or multiple cylinder misfire detected
- P0301Cylinder 1: misfire detected
- P0351Ignition coil A, primary control circuit open
- P0171Mixture too lean (bank 1)
- P0101Mass or volume air flow sensor A, circuit: range/performance
- P0299Turbocharger/supercharger A: underboost
- P2187System (bank 1): too lean at idle
Generic codes that often come with this symptom. Seeing one does not confirm the cause: it is where the diagnosis starts.
How the ECO-LITE helps diagnose it
Plugged into the OBD socket, the ECO-LITE reads the fault codes of the control units that answer, with the freeze-frame data captured when the fault happened, and shows live data on your phone or computer. With your permission, your garage can see them remotely before you bring the car in.
What to look at here: misfire counters, fuel trims, air flow, boost and fuel pressure, if the car reports them.
Frequently asked questions
Can the jerking come from the clutch or the gearbox?
Yes. If the revs rise without the car speeding up, look at the clutch; if the jerks coincide with gear changes on an automatic, the gearbox.
Why does it only jerk when cold?
When cold the mixture is richer and any weak plug, coil or injector shows sooner. So does water condensed in the fuel.
Can there be a code with no warning light?
Yes: many control units store a pending code before lighting the warning. A full reading shows it.
Keep reading
- Engine ignition: how it works and what fails
- Flashing engine warning light: what it means and what to do
- Rough idle: why the engine shakes or hunts when stationary
- Car loses power: what limp mode is
- Car symptoms: what they mean and what to do
- Check engine light on: what to do
- How to read and clear your car's fault codes
- OBD fault codes: what each one means