A rough idle in a car can be caused by a variety of issues, some of which include:
Dirty or clogged air filter: If the air filter is dirty or clogged, it can restrict airflow to the engine, resulting in a rough idle.
Faulty spark plugs: Spark plugs that are worn out or fouled can cause the engine to misfire, leading to a rough idle.
Vacuum leaks: Vacuum leaks can allow unmetered air into the engine, causing a rough idle.
Dirty fuel injectors: Dirty fuel injectors can cause a lean fuel mixture, leading to a rough idle.
Faulty sensors: Faulty sensors, such as the Mass Air Flow (MAF) sensor or the Oxygen (O2) sensor, can cause incorrect readings and lead to a rough idle.
Electrical issues: Electrical problems such as a weak battery or a failing alternator can cause fluctuations in engine speed, leading to a rough idle.
If you are experiencing a rough idle in your car, it is best to take it to a mechanic to diagnose and fix the issue.