Symptoms
- Check engine light illuminated (steady or flashing)
- Engine feels rough, weak, or shaky
- Possible reduced fuel economy
- Possible hesitation or stalling
Likely causes
- CommonCylinder misfireA misfire both triggers the light and causes the rough feeling directly.
- CommonFaulty oxygen or mass airflow sensorBad sensor data throws off the air/fuel mixture the engine relies on to run smoothly.
- PossibleVacuum leakUnmetered air can trigger a fuel trim code and cause a rough idle.
- PossibleFailing catalytic converterSevere restriction can affect running as well as trigger an efficiency code.
- CommonIgnition system problem (coils, plugs, wires)Weak or failing ignition parts cause both the code and the rough feel.
What to do
- Note whether the light is steady or flashing; a flashing light means stop driving soon to protect the catalytic converter.
- Get the code(s) read with an OBD-II scanner at a parts store or with your own scanner.
- Write down or photograph the exact code(s) so a shop or online reference gives an accurate answer.
- Do basic checks first: air filter condition, obvious vacuum hose issues, and spark plug age.
- Address the specific system the code points to rather than guessing randomly.
- Clear the code after the repair and confirm it stays off over normal driving before considering it fixed.
Tools and parts
- OBD-II code reader
Spark plugsSearch: “spark plugs for [year make model]”
Oxygen sensorSearch: “oxygen sensor for [year make model]”
When to call a pro
See a shop if you don't have a code reader or if the code points to something beyond a simple part swap, like fuel trims or compression.
Safety
Use caution
A flashing check engine light with rough running means reduce speed and get it checked soon; a steady light with rough running is still worth prompt attention rather than delay.