Subaru 2009 IMPREZA Service Manual page 1081

5. Intake Manifold Vacuum
A: INSPECTION
1) Warm up the engine.
2) Remove the intercooler. <Ref. to IN(H4DOTC)-
13, REMOVAL, Intercooler.>
3) Disconnect the brake booster vacuum hose from
the intake manifold, and install the vacuum gauge.
4) Install the intercooler. <Ref. to IN(H4DOTC)-13,
INSTALLATION, Intercooler.>
5) Keep the engine at idle speed and read the vac-
uum gauge indication.
By observing the vacuum gauge needle move-
ment, the internal condition of the engine can be di-
agnosed as described below.
Intake manifold vacuum (at idling, A/C OFF):
–68.0 kPa (–510 mmHg, –20.08 inHg) or more
(AT model)
–70.6 kPa (–530 mmHg, –20.85 inHg) or more
(MT model)
Diagnosis of engine condition by measurement of intake manifold vacuum
Vacuum gauge indication
1. Needle is steady but lower than normal position. This tendency
becomes more evident as engine temperature rises.
2. Needle intermittently drops to position lower than normal position.
3. Needle drops suddenly and intermittently from normal position.
4. When engine speed is gradually increased, needle begins to
vibrate rapidly at certain speed, and then vibration increases as
engine speed increases.
5. Needle vibrates above and below normal position in narrow range.
Intake Manifold Vacuum
ME-03897
Leakage around intake manifold gasket, or disconnected
or damaged vacuum hose
Leakage around cylinder
Sticky valve
Weak or broken valve springs
Defective ignition system
ME(H4DOTC)-23
MECHANICAL
Possible engine condition