Car Running Rough and Check Engine Light On

Causes of a Rough Running Engine

Spark plug problems: Worn or fouled spark plugs can cause the engine to misfire, which can lead to a rough idle and loss of power.
Fuel system problems: A clogged fuel filter or a faulty fuel pump can restrict the flow of fuel to the engine, which can cause the engine to run lean or rich.
Airflow problems: A dirty air filter or a clogged intake manifold can restrict the flow of air to the engine, which can cause the engine to run lean.
Compression problems: Worn piston rings or a blown head gasket can cause the engine to lose compression, which can lead to a rough idle and loss of power.
Timing problems: A stretched or broken timing belt or chain can cause the engine’s timing to be off, which can lead to a rough idle and loss of power.

Causes of a Check Engine Light

Oxygen sensor problems: The oxygen sensor monitors the oxygen content of the exhaust gases and sends this information to the engine’s computer. A faulty oxygen sensor can cause the engine to run rich or lean, which can lead to a rough idle and loss of power.
Catalytic converter problems: The catalytic converter converts harmful pollutants in the exhaust gases into less harmful substances. A clogged or damaged catalytic converter can restrict the flow of exhaust gases, which can lead to a rough idle and loss of power.
Evaporative emissions system problems: The evaporative emissions system prevents fuel vapors from escaping into the atmosphere. A faulty evaporative emissions system can cause the engine to run rich, which can lead to a rough idle and loss of power.
Exhaust gas recirculation (EGR) system problems: The EGR system recirculates a portion of the exhaust gases back into the engine. A faulty EGR system can cause the engine to run rich or lean, which can lead to a rough idle and loss of power.
Mass airflow sensor problems: The mass airflow sensor measures the amount of air flowing into the engine. A faulty mass airflow sensor can cause the engine to run rich or lean, which can lead to a rough idle and loss of power.

How to Fix a Rough Running Engine with Check Engine Light On

The first step in fixing a rough running engine with check engine light on is to have the vehicle scanned for trouble codes. The trouble codes will indicate the source of the problem and will help you to determine the necessary repairs.

Once you have the trouble codes, you can begin to repair the problem. If the trouble codes indicate a spark plug problem, you will need to replace the spark plugs. If the trouble codes indicate a fuel system problem, you will need to clean the fuel filter or replace the fuel pump. If the trouble codes indicate an airflow problem, you will need to clean the air filter or replace the intake manifold. If the trouble codes indicate a compression problem, you will need to have the engine rebuilt. If the trouble codes indicate a timing problem, you will need to replace the timing belt or chain.

Once you have repaired the problem, you should reset the check engine light. You can do this by disconnecting the negative battery terminal for 10 minutes and then reconnecting it.

Conclusion

A rough running engine with check engine light on can be caused by a variety of problems. By having the vehicle scanned for trouble codes, you can determine the source of the problem and begin to repair it. Once you have repaired the problem, you should reset the check engine light.