What causes the hissing sound at idle?

[DelLuna]

The reasons for a hissing sound at idle are as follows: 1. Poor spark plug performance; 2. Vacuum hose leakage; 3. High-voltage wire leakage; 4. PCV valve blockage; 5. Throttle position sensor malfunction; 6. Idle stepper motor failure; 7. Idle control valve malfunction; 8. Abnormal throttle opening; 9. Intake system leakage. The causes of valve leakage include: 1. Wear: The working surfaces of the valve and valve seat wear or corrode, forming spots or depressions with carbon buildup. 2. Poor sealing: Excessive clearance between the valve stem and valve guide causes the valve stem to wobble, preventing proper sealing, or the valve stem bends and deforms, tilting the valve head and resulting in leakage.