A vacuum leak can cause a rough idle by allowing unmetered air to enter the engine. This can cause the engine to run lean, which can lead to a number of problems, including a rough idle, stalling, and poor fuel economy. Check for vacuum leaks by spraying a small amount of water around the vacuum lines. If the engine idle changes, then there is likely a vacuum leak.
2. Fuel injector problems
Fuel injector problems can also cause a rough idle. If the fuel injectors are not properly delivering fuel to the engine, it can cause the engine to run lean or rich. This can lead to a rough idle, stalling, and poor fuel economy. Check the fuel injectors by cleaning them with a fuel injector cleaner. If the problem persists, then the fuel injectors may need to be replaced.
3. Spark plug problems
Spark plug problems can also cause a rough idle. If the spark plugs are not properly firing, it can cause the engine to run lean or rich. This can lead to a rough idle, stalling, and poor fuel economy. Check the spark plugs by removing them and inspecting them for damage. If the spark plugs are damaged, then they will need to be replaced.
4. Throttle body problems
Throttle body problems can also cause a rough idle. If the throttle body is not properly controlling the air flow into the engine, it can cause the engine to run lean or rich. This can lead to a rough idle, stalling, and poor fuel economy. Check the throttle body by cleaning it with a throttle body cleaner. If the problem persists, then the throttle body may need to be replaced.
5. Idle air control valve (IAC valve) problems
The IAC valve is responsible for controlling the amount of air that enters the engine at idle. If the IAC valve is not working properly, it can cause the engine to run lean or rich. This can lead to a rough idle, stalling, and poor fuel economy. Check the IAC valve by cleaning it with a throttle body cleaner. If the problem persists, then the IAC valve may need to be replaced.
