What is the function of the IAC valve in an Emission Control System?

• A. It regulates fuel pressure to the engine.
• B. The IAC valve helps to control the formation of NOx emissions.
• C. It monitors exhaust temperature.
• D. It controls ignition timing.

Answer: (B)

The IAC valve controls how much air bypasses the throttle at idle, letting the engine idle at a stable speed with the right air–fuel mix. By fine-tuning idle air, it keeps combustion temperatures and the engine load within a range that minimizes emissions, including NOx, and helps the catalytic converter work effectively during idle conditions. It doesn’t regulate fuel pressure (that’s a fuel pressure regulator), monitor exhaust temperature (that’s an exhaust gas temperature sensor), or control ignition timing (that’s done by the ignition system).