From the RAVE
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Vacuum Enhancer System
Vehicles from 2003 model year – The vacuum enhancer solenoid valve is no longer fitted to vehicles from 2003
model year onwards. On these vehicles the solenoid valve is removed, but the venturi valve and associated piping is
retained. On this system the vacuum enhancement is still required, but due to the deletion of the air assist injectors,
the vacuum enhancement can be permanently operated.
The vacuum enhancer system increases the relatively low vacuum available from the inlet manifold to increase
braking assistance. The system consists of a venturi valve, a solenoid valve and associated pipes.
The venturi valve is installed in the vacuum pipe between the brake servo and the inlet manifold. An air feed pipe,
from the intake duct upstream of the throttle body via the solenoid valve, is also connected to the venturi valve. Internal
ducts in the venturi valve connect the brake servo and air feed ports to the inlet manifold port. The duct connecting
the air feed port to the inlet manifold port incorporates the venturi. A check valve, integrated into the brake servo port,
prevents the reverse flow of air and fuel vapour to the brake servo.
The solenoid valve controls the air feed to the venturi valve. Operation of the solenoid valve is controlled by the ECM.
To improve engine idle speed refinement, when the gearbox lever is in Park or Neutral, the solenoid valve is closed
and the brake servo senses the vacuum in the inlet manifold via the venturi valve. When the gearbox lever is selected
to positions other than Park or Neutral, the ECM energises the solenoid valve and air from the upstream side of the
throttle body is fed to the venturi valve. The air flows through the venturi valve into the inlet manifold. As the air flows
through the venturi in the venturi valve, it increases in velocity and decreases in pressure, resulting in an increase in
the vacuum sensed by the brake servo. Depending on ambient conditions and"