Subaru Legacy 2004 Service Manual page 1133

MECHANICAL
5. Intake Manifold Vacuum
A: INSPECTION
1) Remove the collector cover.
2) Idle the engine.
3) Disconnect the brake vacuum hose from intake
manifold, and then install the vacuum gauge.
4) Keep the engine at idle speed and read the vac-
uum gauge indication.
By observing the gauge needle movement, internal
condition of the engine can be diagnosed as de-
scribed below.
Vacuum pressure (at idling, A/C "OFF"):
# #
66.7 kPa ( 500 mmHg,
Diagnosis of engine condition by measurement of intake manifold vacuum
Vacuum gauge indication
1. Needle motion is steady but lower than normal position. This
tendency becomes more evident as engine temperature rises.
2. When engine speed is reduced slowly from higher speed,
needle stops temporarily when it is lowering or becomes steady
above normal position.
3. Needle intermittently drops to the lower position than normal. Leakage around cylinder
4. Needle drops suddenly and intermittently from normal posi-
tion.
5. When engine speed is gradually increased, needle begins to
vibrate rapidly at certain speed, and then vibration increases as
engine speed increases.
6. Needle vibrates above and below normal position in narrow
range.
Intake Manifold Vacuum
ME-00801
#
19.70 inHg) or less
ME(H4DOTC)-24
Possible engine condition
Leakage around intake manifold gasket, or disconnected or
damaged vacuum hose
Back pressure too high, or exhaust system clogged
Sticky valve
Weak or broken valve springs
Defective ignition system or throttle chamber idle adjustment