Engine Vacuum Gauge Interpreter

Sea level warm idle: roughly 17 to 22 inHg.
Altitude adjustment: expected vacuum drops about 1 inHg per 1,000 feet.
Healthy snap test: quick drop, then rebound above idle before settling.

Use old-school vacuum readings to quickly narrow modern drivability faults.

Interpret Your Vacuum Test

Warm idle vacuum (inHg):

Test altitude (ft, optional):

Needle behavior at idle:

Snap-throttle response:

Gauge while holding ~2500 RPM:

Run this test on a fully warm engine, parked safely, with vacuum source connected to intake manifold vacuum.