Coasting Valve

With vacuum gauge installed in line from air control valve to coasting valve, start and warm up engine. At idle speed (transmissions in neutral), the vacuum reading should be more than 15.7" of mercury.
Raise engine speed to about 2500 RPM. When throttle valve is now closed suddenly, gauge reading should be 0-1.18" of mercury. When engine speed is lowered from 2500 RPM to 1150-1250 RPM (Man. Trans.) or 1350-1450 RPM (Auto. Trans.), vacuum reading should be more than 15.7" of mercury.

Fig 1: CHECKING NO. 1 CONTROL BOX (COASTING VALVE)
Courtesy of MAZDA MOTORS CORP.

Fig 2: TESTING COASTING VALVE
Courtesy of MAZDA MOTORS CORP.
If vacuum gauge readings are excessive, check that solenoid operates properly and that there is no clogging in the vacuum relief passage connecting vacuum chamber and air inlet pipe in coasting valve. Check for correct current flow to coasting valve solenoid. See NO. 1 CONTROL BOX .