Passat L4-1984cc 2.0L DOHC (9A) (1990)
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Air Flow Meter/Sensor: Description and Operation
CO. Adjustment Screw
CIS-E CO Adjustment Screw
The CO Adjustment Screw can only be reached and adjusted after removing the anti-tampering plug in the top of the air flow sensor housing. This is a
small plug with a soft aluminum top and a hard steel bottom, removed by drilling a 3/32 (2.5 mm) hole in the aluminum and using a sheet metal screw to
extract the plug.
The CO Adjustment Screw raises or lowers the position of the fuel distributor control plunger relative to the air flow sensor plate. With the
anti-tampering plug removed, the adjustment is made using a long (approx. 4 in.) 3 mm hex wrench. Turning the CO Adjustment Screw clockwise will
make the mixture richer (higher % CO) and lowers the differential pressure regulator current. Turning the CO Adjustment Screw counterclockwise will
make the mixture leaner (lower % CO) and increases the differential pressure regulator current.
The fuel mixture should only be adjusted if the % CO is found to be outside the specified range. It must only be made in accordance with differential
pressure regulator current, and only after confirming that ignition timing and idle speed are within specifications.
