ENGINE STATE VACUUM GAUGE READING INDICATION
Steady idle (800-1200rpm) Gauge steady, 17-22 Normal & healthy
Steady idle (800-1200 rpm) Intermittently drops several needle divisions Sticking valve or broken valve spring
Steady idle (800-1200 rpm) Steady, low reading, 8-14 Small vacuum leak or valve timing off; could have low compression/worn rings (verify with a compression or leakdown test).
Steady idle (800-1200 rpm) Steady, low reading, under 8 Vacuum leak (check brake booster, vacuum lines, etc.)
Idle (800-1200 rpm) Needle drops sharply on a regular rhythm Burnt valve, or a valve with clearance too tight
Idle (800-1200 rpm) Needle drifts up & down, along with rpm drift Mixture off or small vacuum leak
Idle (800-1200rpm) Vacuum gradually drops Excessive exhaust back pressure (plugged muffler or catalytic converter)
Idle (800-1200rpm) Intermittent fluctuation Ignition miss; sticking valve
Idle (800-1200rpm) Steady, above 22 Ignition timing may be too advanced
Open & close throttle quickly Drops to about 2, jumps to about 25 Healthy engine
Open & close throttle quickly Drops to 0, jumps to about 20 May confirm worn rings (especially if idle shows only about 15-20) Verify with a compression or leakdown test.
Sunday, July 4th, 2010 AT 3:35 AM