Symptoms suggesting a bad IAC valve:
* Rough idle: The engine shakes or vibrates excessively at idle. This is often the most common symptom.
* Stalling: The engine stalls, especially at idle or when coming to a stop.
* High idle: The engine idles at a much higher RPM than normal (typically above 1000 RPM).
* Idle speed fluctuation: The engine idle speed constantly jumps up and down.
* Poor fuel economy: While not always indicative of a solely bad IAC valve, it can contribute to lower MPG.
* Hard starting: Sometimes, the engine will be difficult to start, especially when it's cold.
* Check engine light: A check engine light will likely illuminate, usually with a code related to idle speed or air intake.
How to investigate further (requires some mechanical aptitude):
* Visual inspection: Inspect the IAC valve for any visible damage, such as cracks, corrosion, or debris. This is usually located near the throttle body.
* Check the IAC valve connector: Ensure the connector is securely connected and not damaged.
* Advanced diagnostics (requires a multimeter and some understanding of automotive electrical systems): You can test the IAC valve's electrical continuity and resistance using a multimeter to check if it's getting power and responding correctly. However, this requires technical knowledge and is more complex.
* OBD-II scan: A scan tool can retrieve diagnostic trouble codes (DTCs) from the car's computer. Certain codes point directly to problems with the IAC valve or related systems.
Important Note: It's crucial to remember that these symptoms can be caused by other issues, including problems with the throttle position sensor, mass airflow sensor, vacuum leaks, or other engine components. A proper diagnosis requires a systematic approach, possibly involving a professional mechanic. Don't just assume it's the IAC valve based on one or two symptoms.
