Volkswagen 2004 Jetta, Introduction Manual

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44
Engines
Overrun Air Divert Control
If the throttle valve closes when the engine
is in overrun, back pressure develops in the
turbo housing. Back pressure reduces the
speed of the turbine, which reduces boost
pressure and increases turbo lag.
To avoid this, the Turbocharger Recirculating
Valve N249 is opened by an electrical
actuator. This allows the compressed air to
flow back to the intake side of the circuit
through the turbine. This maintains turbine
speed. The Turbocharger Recirculating Valve
N249 closes when the throttle valve opens
again and boost pressure is immediately
available.
Overrun Mode
Divert Air Valve Open
Divert Air
Valve Closed
Engine Running Under Load
Air Intake
From Air
Filter
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