E da, ovo veli google...A hissing sound when releasing the throttle pedal on a Volkswagen Polo, especially a turbocharged model, is often caused by a turbocharger's diverter valve or a vacuum leak. The diverter valve releases excess boost pressure when you lift off the accelerator, and it's normal to hear a "shhhh" sound as it vents. However, a leak in the intake system or a faulty diverter valve can also cause a hissing or whistling noise.
Here's a more detailed breakdown:
Turbocharger Diverter Valve:
In turbocharged engines, the diverter valve (also called a bypass valve or
-off valve) diverts excess boost pressure back into the intake system when you lift off the accelerator. This prevents a sudden pressure surge and potential damage to the turbocharger. A hissing sound is often a normal part of this process.
Vacuum Leaks:
Leaks in the vacuum hoses or the ducting between the mass airflow sensor and the throttle body can also cause hissing. These leaks can become more noticeable when the throttle is released, as the engine's vacuum changes.
Other Potential Causes:
While less common, a hissing sound could also be related to a leak in the exhaust system, a faulty brake booster, or even a failing air conditioning compressor.
Troubleshooting:
1. Listen carefully:
Try to pinpoint the exact location of the hiss. Is it coming from the engine bay, under the car, or near the brakes?
2. Check the hoses:
Inspect the vacuum hoses and intake ducting for any signs of damage, cracks, or loose connections.
3. Consider the turbo:
If it's a turbocharged engine, ensure the diverter valve is functioning correctly and not leaking.
4. Consult a mechanic:
If you're unable to identify the source of the hiss or if the noise is accompanied by other symptoms (like reduced power or rough idling), it's best to have a qualified mechanic inspect the car.
