Volkswagen Front Wheel Drive 1974-1989 Repair Guide

Air/Fuel Mixture Adjustment

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ADJUSTMENT



The air/fuel mixture is measured by sampling the exhaust with a CO meter. If this equipment is not available, no checking or adjustment is possible. Since adjusting the mixture is not part of a normal tune-up, the adjusting screw is protected with a tamper-proof plug. If the air/fuel ratio is obviously incorrect (lean miss, sooty spark plugs and tailpipe), or if the CO measurement is out of specification, look for other problems such as a vacuum leak, bad sensors, loose electrical connections, and correct any faults before deciding to adjusting the mixture.

  1. With the engine at normal operating temperature, make sure the ignition timing and idle speed are correct. Stop the engine.
  2.  
  3. Unplug the blue coolant temperature sensor connector.
  4.  
  5. Raise the dipstick slightly to allow for crankcase ventilation. Clamp the crankcase breather hose near its control valve.
  6.  
  7. Start the engine and measure the CO content; it must read 0.3-1.1 percent. If adjustment is necessary, remove the mixture adjusting screw plug as follows:
    1. Center-punch the mixture adjusting screw plug.
    2.  
    3. Drill a 3 / 32 in. (2.5mm) hole approximately 5 / 32 in. (4mm) deep in the center of the plug. It is helpful to apply a small amount of grease to the drill bit to catch the metal shavings.
    4.  
    5. Thread a 1 / 8 in. (3mm) sheet metal screw into the hole.
    6.  
    7. Remove the plug using a pair of pliers.
    8.  

  8.  
  9. Insert a 5mm Allen wrench in the hole. Adjust the CO to the proper level following the graph.
  10.  
  11. When adjustment is completed, carefully drive a new plug into the adjusting hole.
  12.  

 
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