Fast Idle Thermo Valve

Remove fast idle thermo valve cover. Ensure engine coolant temperature is less than 86°F (30°C). Start engine and allow to idle. Place finger over valve seat area. See Fig 1 . If air flow is present at valve seat area, go to next step. If air flow is not present, replace fast idle thermo valve and recheck for symptom.
Start engine and run at 3000 RPM with no loads and transmission in Park or Neutral, until radiator fan comes on. Allow engine to idle. Fast idle thermo valve should be completely closed. Place finger on valve seat area. If vacuum is felt, fast idle thermo valve is leaking. Ensure engine coolant level is correct and cooling system is free of air. If okay, replace fast idle thermo valve and recheck for symptom.
NOTE: If fast idle thermo valve was removed, perform PCM reset procedure. See PCM RESET PROCEDURE/CLEARING CODES in the TESTS W/CODES article.

Fig 1: Fast Idle Thermo Valve Seat (Typical)
Courtesy of AMERICAN HONDA MOTOR CO., INC.

NOTE: For Idle Air Control (IAC) valve information and test procedures, see the TESTS W/CODES article.