Intake Manifold Vacuum - Subaru 2002 IMPREZA Service Manual

INTAKE MANIFOLD VACUUM
MECHANICAL
Vacuum gauge indication
1. Needle is steady but lower than normal position. This ten-
dencv becomes more evident as enaine temperature rises.
5. Intake Manifold Vacuum
Possible engine condition
Leakage around intake manifold gasket or disconnection or
damaaed vacuum hose
A: INSPECTION
1) Warm-uD the enuine.
6. Needle vibrates above and below normal position in narrow
range.
3) Keep the engine at the idle speed and read the
vacuum gauge indication.
By observing the gauge needle movement, the in-
ternal condition of the engine can be diagnosed as
Defective ignition system or throttle chamber idle adjustment
2) Disconnect the b a k e vacuum hose and install
described below.
Vacuum pressure (at idling, A/C
"OFF):
Less than -60.0 kPa (-450 mmHg, -1 7.72 in-
I
Diagnosis of engine condition by measurement of manifold vacuum
~
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 position lower than normal
position.
Back pressure too high, or exhaust system clogged
Leakage around cylinder
4. Needle drops suddenly and intermittently from normal posi-
vibrate rapidly at certain speed, and then vibration increases as
enaine speed increases.
Sticky valves
Weak or broken valve springs
ME(D0HC TURBO)-25