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Home >> Mazda >> 1978 >> Cosmo Automatic Trans >> Repair and Diagnosis >> Engine Performance >> Engine Control Systems >> Exhaust Emissions System - Deceleration Control System - Rotary Engines >> Testing >> Deceleration Control Valve >> 1975 Models
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1975 Models

  1. Turn ignition on. Unplug connector at both solenoids. A "clicking" sound should be heard from both solenoids when disconnected. If not, replace solenoid(s).
  2. Connect tachometer to engine. Start and run engine at idle. Disconnect air hose from deceleration control valve at air cleaner. Block air hose opening with hand. See Figure. Engine speed should not change noticeably.
  3. Block air hose opening with hand. Rapidly accelerate engine to 4000 RPM and quickly release throttle. Vacuum should be felt at end of hose for 1-1 1/2 seconds, tapering off until engine reaches 1150 RPM.
    NOTE: On manual transmission equipped vehicles, only a small amount of vacuum may be noted.
  4. On manual transmission equipped vehicles, disconnect coasting valve solenoid and apply 12 volts to terminal. Disconnect idle switch and connect a voltmeter to power lead of coasting valve solenoid.
  5. Slowly decrease engine speed from 2000 RPM and record RPM at which current starts to flow. Current should start to flow at 1050-1250 RPM and continue to flow until idle speed is reached. Slowly increase engine speed and record RPM at which current stops flowing. Speed should be within 80-220 RPM of current flow RPM.
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