A car that jerks while accelerating may have a dirty fuel system, bad spark plugs, or a transmission problem. Have it checked.
Common causes
- Dirty fuel injectors or old fuel filter.
- Worn spark plugs or ignition coil.
- Dirty mass airflow sensor.
- Clogged catalytic converter.
- Transmission problems.
Check
Is the check engine light on? A code reader tells which cylinder misfires.
What to do
Replace spark plugs (every 30,000 to 100,000 miles) and use fuel cleaner.
See a mechanic
If jerking continues, as a misfire can damage the catalytic converter.
Fuel system
- Dirty or clogged fuel filter.
- Failing fuel pump.
- Clogged fuel injectors.
- Poor quality fuel or water in fuel.
Ignition system
- Worn spark plugs.
- Bad ignition coils or plug wires.
- Misfires, which cause hesitation or jerking, often with a flashing check engine light.
Air intake and sensors
- Dirty mass airflow (MAF) sensor.
- Faulty throttle position sensor.
- Dirty throttle body.
- Vacuum leaks.
- Oxygen sensor failure.
Exhaust
A clogged catalytic converter restricts exhaust and reduces power, causing jerking and sometimes a rotten egg smell.
Transmission
- Low or dirty transmission fluid.
- Worn clutch in a manual car.
- Failing torque converter or solenoids in an automatic.
- Shifting problems, slipping or harsh shifts.
Check engine light
Read trouble codes with an OBD-II scanner (many parts stores will do it free). A code like P0300 indicates random misfires.
What to do
- Check the gas cap and fuel level.
- Replace the air filter if dirty.
- Use fuel injector cleaner as a basic step.
- Follow your maintenance schedule for spark plugs (every 30,000 to 100,000 miles depending on type).
- Avoid heavy acceleration until the problem is fixed.
See a mechanic
If the check engine light is flashing, the jerking is severe, or it comes with shaking, loss of power or transmission slipping. Continued driving with misfires can damage the catalytic converter, a repair that can cost 1,000 to 3,000 dollars or more.
Likely mechanical causes
A car that jerks when accelerating may have a misfire from worn spark plugs or failing ignition coils, a dirty or failing mass airflow sensor, clogged fuel injectors, a weak fuel pump or a clogged fuel filter. A restricted catalytic converter can choke exhaust and cause power loss. In automatic cars, a slipping transmission or low or dirty transmission fluid can cause surging and jerking, and torque converter problems may be the cause. A vacuum leak can also upset the air to fuel mix.
What to do
Check whether the check engine light is on, and get codes read, as many parts stores do so for free. Look at the fuel level, replace old plugs at the interval in the manual, which is often 60,000 to 100,000 miles, and consider cleaning the throttle body. A flashing check engine light with jerking means a severe misfire, so reduce speed and have the car checked soon to protect the catalytic converter. Repair costs range from about 100 USD for plugs to over 1,000 USD for fuel pumps or transmission work. See a mechanic if the problem persists.
Based on data from AAA and vehicle service guides
