When my throttle snaps closed, there is a brief whoosh or whistle sound from the air filter area. What is causing this?
When the engine is loaded, very high turbine speeds are required for the turbo charger to provide intake manifold boost. When the fuel is suddenly cut off, the exhaust volume collapses and the turbocharger rapidly spins down. As the turbine looses speed, it looses it’s ability to sustain the manifold pressure and compressed air rushes backward from the manifold and through the turbocharger. The momentary airflow reversal is not harmful and produces the short pSSHTT sound.
