INTAKE MANIFOLD VACUUM
Mechanical
5. Intake Manifold Vacuum
S183654
3) Keep the engine at the idle speed and read the vacuum gauge indication. By observing the gauge needle movement, the internal condition of the engine can be diagnosed as described below.
A: INSPECTION
S183654A10
1)  Warm-up the engine.
2)   Disconnect the brake vacuum hose and install the vacuum gauge to the hose fitting on the manifold.
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Vacuum pressure (at idling, A/C "OFF"):
Less than -60.0 kPa (-450 mmHg, -17.72 inHg)
Diagnosis of engine condition by measurement of manifold vacuum
Vacuum gauge indication
Possible engine condition
1. Needle is steady but lower than normal position. This tendency becomes more evident as engine temperature rises.
Leakage around intake manifold gasket or disconnection or damaged vacuum hose
2. When engine speed is reduced slowly from higher speed, needle stops temporarily when it is lowering or becomes steady above normal position.
Back pressure too high, or exhaust system clogged
3. Needle intermittently drops to position lower than normal position.
Leakage around cylinder
4. Needle drops suddenly and intermittently from normal position.
Sticky valves
5. When engine speed is gradually increased, needle begins to vibrate rapidly at certain speed, and then vibration increases as engine speed increases.
Weak or broken valve springs
6. Needle vibrates above and below normal position in narrow range.
Defective ignition system or throttle chamber idle adjustment
4) After measuring intake manifold vacuum, install brake vacuum hose.
ME(DOHC TURBO)-25