Vacuum leak: Replacing the PCV valve can disturb or create vacuum leaks around the PCV valve or other related vacuum lines. A vacuum leak can cause the engine to run lean, which can lead to an increased idle speed. Check for any disconnected or cracked vacuum lines and ensure everything is connected properly.
Dirty throttle body: A dirty throttle body can also cause increased idling. When the throttle body gets dirty, it can hinder the proper flow of air into the engine, leading to high idling. Try cleaning the throttle body and its surroundings to see if that resolves the issue.
Malfunctioning IAC valve: The idle air control (IAC) valve regulates the amount of air that bypasses the throttle body to control the idle speed. If the IAC valve is faulty or has carbon buildup, it can cause the engine to idle high. Cleaning the IAC valve or replacing it, if necessary, might solve the problem.
ECU needs to relearn idle: In some cases, after replacing the PCV valve, the engine control unit (ECU) needs to relearn the optimal idle speed. Driving the car for a while or performing an idle relearn procedure (if specified by your vehicle's manufacturer) can allow the ECU to adjust and bring the idling back to normal.
If you've checked all these potential causes and still experiencing high idling, it's recommended to consult with a qualified mechanic or automotive technician who can conduct further diagnostics and identify the exact root of the problem.
