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Home >> Audi >> 1992 >> 100 CS, 2.8 K, Standard >> Repair and Diagnosis >> Engine Performance >> Engine Controls - Adjustments >> Idle Speed & Mixture

Idle Speed & Mixture

NOTE: Mixture adjustment is not a part of normal tune-up procedure and should not be performed unless mixture control unit is replaced or vehicle fails emissions testing.
NOTE: Idle speed is electronically controlled and cannot be adjusted.
  1. Ensure engine is at normal operating temperature. Turn ignition off. Ensure all electrical accessories and cooling fan are off. Remove adjustment screw cap and pry out plastic plug from CO potentiometer installed in MAF housing. See Fig 1 .
  2. Connect CO tester to CO tap tube on right exhaust manifold. See Fig 2 . Read and record CO content. Repeat test on left CO tap tube. Content must be 0.3-1.2% by volume.
    Fig 1: Locating CO Potentiometer
    G93F79256Courtesy of AUDI OF AMERICA, INC.
    Fig 2: Locating CO Tap Tube
    G93F79280Courtesy of AUDI OF AMERICA, INC.
  3. If CO content is less than 0.3% by volume, eliminate leak in area of CO tap tube or adaptor.
  4. If CO content is more than 1.2% by volume, eliminate leak in exhaust system between engine and HO2S.
  5. Install a NEW plastic plug over CO adjusting screw. Press on the cap.
  6. Check idle speed. Idle RPM must be within specification. See IDLE SPEED & CO LEVEL SPECIFICATIONS table. If idle speed is not within specification, check air intake system for leaks. Idle speed is electronically controlled and is not adjustable.
    IDLE SPEED & CO LEVEL SPECIFICATIONS

    Application Idle RPM CO Level
    Checking Value 720-860 0.3-1.2%
  7. If necessary, check differential pressure regulator current with oxygen sensor connected. Reading must fluctuate between -4 and 6 mA and CO level must be 0.3-1.2%.
NOTE: If idle speed drops severely when A/C system is turned on, check idle stabilization system.
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