Ignition System:
* Spark Plugs: Worn, fouled, or damaged spark plugs are a frequent cause. They may be misfiring, causing a cylinder to not fire properly.
* Ignition Wires/Coils: Damaged or worn ignition wires can prevent a strong spark from reaching the spark plug. Similarly, faulty ignition coils can fail to deliver sufficient voltage.
* Distributor Cap and Rotor (older vehicles): Cracks or corrosion in these components can disrupt the spark delivery.
Fuel System:
* Fuel Injectors: Clogged or malfunctioning fuel injectors can deliver an inconsistent fuel/air mixture.
* Fuel Filter: A clogged fuel filter restricts fuel flow, leading to insufficient fuel reaching the engine.
* Fuel Pump: A weak or failing fuel pump may not provide enough fuel pressure.
* Low Fuel: Surprisingly, simply having low fuel can sometimes cause rough running.
Air Intake System:
* Air Filter: A dirty air filter restricts airflow, leading to a lean fuel mixture.
* Vacuum Leaks: Leaks in the intake system can disrupt the proper air/fuel mixture.
Engine Mechanical Issues:
* Worn or Damaged Valves: Worn valve seats or damaged valves can lead to compression loss and rough running.
* Low Compression: Low compression in one or more cylinders indicates a problem with the valves, piston rings, or head gasket.
* Camshaft Issues: A worn or damaged camshaft can affect valve timing and lead to a rough idle.
* Timing Belt/Chain Issues: A broken or slipped timing belt/chain will cause severe engine damage and very rough running (or no running at all).
Other Potential Causes:
* Oxygen Sensor: A faulty oxygen sensor provides incorrect information to the engine control unit (ECU), leading to a poor air/fuel mixture.
* Mass Airflow Sensor (MAF): A dirty or faulty MAF sensor can also provide incorrect information to the ECU.
* Engine Control Unit (ECU): While less common, a faulty ECU can cause a range of issues, including rough running.
* Exhaust System Restrictions: A severely clogged catalytic converter or muffler can restrict exhaust flow, leading to rough running.
Troubleshooting:
Diagnosing the exact cause requires a systematic approach. Start by checking the easily accessible items like the air filter, spark plugs, and fuel filter. If the problem persists, you may need to use a scan tool to read diagnostic trouble codes (DTCs) from the ECU or seek professional help from a mechanic. They have specialized tools and experience to pinpoint the issue.
