Acura 16500-P0A-A51 Fast Idle Valve Assembly (Af42D)

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When the engine is idling, the air/fuel ratio is managed by the Idle Air Control (IAC) system, which includes the Powertrain Control Module (PCM), the IAC valve, and for certain models, the fast idle thermo valve. The IAC valve is regulated by the PCM based on various engine conditions, controlling airflow past the throttle plate into the intake manifold. The PCM adjusts the idle speed using data from multiple sensors, ensuring smooth operation during engine start-up by opening the IAC valve to allow extra air. Different types of IAC valves are utilized across models, with rotary valves on certain automatic transaxle Civics and linear valves on manual transaxle Civics and other models. To check the IAC valve, the parking brake should be applied, wheels blocked, and the transaxle placed in Neutral or Park. After starting the engine and holding it at 3,000 rpm until the coolant fan activates, the IAC valve's electrical connector should be disconnected to observe idle speed changes. If the idle speed increases for rotary valves or drops for linear valves, the IAC valve may be functioning correctly; otherwise, it may be defective. Further testing involves measuring voltage at the IAC valve connector and checking for continuity in the wiring. If the IAC valve is confirmed to be operational, the PCM and electrical circuit should be evaluated by a professional. For replacement, the electrical connector must be disconnected, coolant hoses removed and plugged, and the valve unscrewed from its mounting. Installation follows the reverse order, ensuring a new O-ring is used and coolant levels are checked.

Suction should be felt at the FIT valve port.