A car that jerks, hesitates or shakes when accelerating usually has an engine problem such as a misfire from worn spark plugs or a failing coil, a fuel or air delivery problem, or a drivetrain problem such as a slipping or harsh-shifting transmission, torque converter shudder, worn engine mounts or a worn CV axle. When the jerk happens, and whether a warning light comes on, narrows it down quickly.
Narrow it down by when it happens
| When it happens | Likely causes |
|---|---|
| Stumbles or jerks under load, check engine light on or flashing | Misfire: plugs, coils, injectors |
| Hesitates when you press the pedal | Fuel delivery, dirty mass airflow sensor, vacuum leak, throttle problems |
| Jerks as the transmission shifts | Low or worn fluid, solenoids, worn clutches |
| Shudder at light throttle around 30 to 50 mph | Torque converter clutch shudder |
| Shakes only while accelerating, smooth when coasting | Worn inner CV joint, engine or transmission mounts |
| Vibration that grows with speed | Tire balance, a bent wheel, driveshaft or U-joints |
Engine causes
- Misfire: worn spark plugs, a failing ignition coil or a clogged injector make a cylinder skip, felt as a jerk or stumble. See engine misfire and a flashing check engine light.
- Fuel delivery: a weak fuel pump or clogged filter starves the engine under load.
- Air: a dirty mass airflow sensor or a vacuum leak upsets the mixture.
- Boost problems on turbo and supercharged engines; the computer may cut power, see limp mode.
Transmission causes
- Low or worn fluid: check the level and condition first; see how to check transmission fluid and transmission fluid color.
- Shift solenoids and control: harsh or erratic shifts; see transmission solenoid symptoms.
- Slipping clutches: engine speed flares between gears; see transmission slipping.
- Torque converter shudder: a rumble-strip vibration at light throttle; see torque converter shudder.
Drivetrain and mounts
Worn engine or transmission mounts let the drivetrain rock, which feels like a clunk or jerk when you get on the throttle. A worn inner CV joint on a front-wheel-drive car shakes under acceleration and smooths out when coasting; on rear-wheel-drive trucks, worn U-joints or an unbalanced driveshaft cause vibration. Tire balance and bent wheels cause vibration that grows with speed rather than with throttle.
What to do
- Read any stored codes with a scan tool.
- Check engine oil, coolant and transmission fluid.
- Note when it happens: cold or warm, under load or cruising, while shifting.
- If the check engine light is flashing, ease off and get it diagnosed promptly; a severe misfire can damage the catalytic converter.
If the transmission turns out to be worn, find a replacement by code on our transmissions page; every unit we carry comes with a torque converter.
More guides: bad spark plug symptoms · bad ignition coil symptoms · engine sputtering · transmission shifting hard · car shakes when accelerating · car hesitates when accelerating · car loses power when accelerating.
Trouble codes: P0300 Random/Multiple Misfire · P0121 Throttle Position Sensor Range · P2135 Throttle Position Sensor Correlation · all OBD2 codes.
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