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Home >> Mercedes Benz >> 1987 >> 300E >> Repair and Diagnosis >> Engine Performance >> System >> BOSCH Cis-E System >> Component Testing >> Cold Start System >> Auxiliary Air Valve
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Auxiliary Air Valve

  1. Check switch-off point of auxiliary air valve. With coolant temperature below 70°F (20°C), engine should idle at 900-1200 RPM. Idle RPM should drop to normal when operating temperature reaches 160°F (70°C).
  2. If cold start idle is too low, compress connecting hose between idle speed air distributor and auxiliary air valve. If no RPM change occurs, auxiliary air valve is defective.
  3. If idle RPM is too high at operating temperature, pinch connecting hose between idle speed air distributor and auxiliary air valve. If idle speed changes, auxiliary air valve is sticking or heating element is not functioning.
  4. Check voltage and resistance of auxiliary air valve. Voltage should be 12 volts and resistance should be 40 ohms.
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