1. Faulty spark plugs: Spark plugs that are worn out or damaged can cause the engine to misfire, resulting in a rough idle.
2. Vacuum leaks: A vacuum leak can cause a lean air-fuel mixture, which can lead to a rough idle. Vacuum leaks can occur in various places, such as the intake manifold gasket, vacuum hoses, or brake booster.
3. Dirty or clogged fuel injectors: Dirty or clogged fuel injectors can cause the engine to run lean or misfire, resulting in a rough idle.
4. Faulty idle air control (IAC) valve: The IAC valve regulates the amount of air that bypasses the throttle valve to maintain a steady idle speed. A faulty IAC valve can cause the idle speed to fluctuate or become too low, resulting in a rough idle.
5. Incorrect fuel pressure: Too high or too low fuel pressure can cause the engine to run lean or rich, leading to a rough idle.
6. Damaged oxygen sensor: The oxygen sensor provides feedback to the engine control unit (ECU) about the oxygen content in the exhaust gases. A damaged oxygen sensor can cause the ECU to make incorrect adjustments to the fuel mixture, resulting in a rough idle.
7. Dirty or clogged throttle body: A dirty or clogged throttle body can restrict airflow and cause the engine to idle roughly.
8. Faulty ignition coil or ignition wires: A faulty ignition coil or worn-out ignition wires can cause misfires, leading to a rough idle.
9. Failing EGR valve: A malfunctioning EGR(Exhaust Gas Recirculation) valve might disturb proper idling by re-introducing excessive exhaust gas or not diverting fumes at suitable moments causing hard idling.
