Regulating Valve (Performance Test)
Remove air hose in front of valve. At idle speed, no air must pass through valve. In case of a leaky valve, air will leak into intake manifold causing uneven idling or stalling of engine. When returning to idle speed following brief acceleration, valve should draw air for approximately 1/2 - 1 second. A valve jammed in closed position causes backfire on deceleration.
NOTE:
Both above tests can be performed with a vacuum gauge used in the following manner: Remove air hose in front of valve and connect vacuum gauge. At idle speed reading should show no vacuum. Vacuum reading must be present for 1/2 - 1 second when quickly returning to idle speed after accelerating.