* Rough Idle: The engine shakes excessively, vibrates strongly, or sounds uneven. This is often caused by:
* Spark plug issues: Worn, fouled, or damaged spark plugs can cause misfires, leading to a rough idle.
* Ignition system problems: A failing ignition coil, distributor cap, or rotor can also cause misfires.
* Vacuum leaks: Leaks in the intake manifold or vacuum hoses disrupt the air-fuel mixture, resulting in a rough idle.
* Dirty or clogged fuel injectors: Fuel injectors that are dirty or clogged can deliver an inconsistent fuel spray.
* Faulty mass airflow sensor (MAF): This sensor measures the amount of air entering the engine, and a faulty one can lead to a poor air-fuel mixture.
* Problems with the throttle body: A dirty or malfunctioning throttle body can affect idle speed.
* Low compression in one or more cylinders: This indicates a significant internal engine problem.
* High Idle: The engine runs faster than normal at idle. This might be due to:
* Faulty idle air control (IAC) valve: This valve regulates air flow at idle.
* Throttle position sensor (TPS) issue: This sensor tells the computer the throttle position; a faulty one can cause the engine to idle too high.
* Vacuum leaks: Again, these can also cause a high idle.
* Sticking throttle plate: The throttle plate might not be closing fully.
* Low Idle: The engine struggles to stay running or idles too slowly. This could be related to:
* Low fuel pressure: Insufficient fuel pressure can cause the engine to stall or have a low idle.
* Vacuum leaks: These can impact the engine's ability to maintain idle speed.
* Dirty or clogged fuel filter: Restricts fuel flow.
* Irregular Idle (Hunting): The idle speed fluctuates up and down erratically. This often points to issues with the engine's computer system, sensors or actuators trying to compensate for a problem.
In short, a "funny" idle isn't a specific diagnosis, but a symptom that requires further investigation. It's best to take your car to a mechanic to diagnose the underlying cause. Ignoring the problem can lead to more serious engine damage.
