Subaru IMPREZA GD 2007 Series Manual page 2430

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5. Intake Manifold Vacuum
A: INSPECTION
1) Warm-up the engine.
2) Disconnect the brake vacuum hose from intake manifold, and then install the vacuum gauge.
3) Keep the engine at idle speed and read the vacuum gauge indication.
By observing the gauge needle movement, the internal condition of the engine can be diagnosed as de-
scribed below.
Vacuum pressure (at idling, A/C OFF)
Less than –60.0 kPa (–450 mmHg, –17.72 inHg)
Diagnosis of engine condition by measurement of intake manifold vacuum
Vacuum gauge indication
1. Needle is steady but lower than normal position. This ten-
dency 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 posi-
tion.
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-00008
Leakage around intake manifold gasket, or disconnected or
damaged vacuum hose
Leakage around cylinder
Sticky valve
Weak or broken valve springs
Defective ignition system or throttle chamber idle adjustment
ME(H4DOTC)-29
MECHANICAL
Possible engine condition