Warm up the engine to operating temperature.
Clamp the hose going to the idle speed control valve move.
Disconnect the crankcase ventilation hose from the cylinder head cover.
Use the idle speed adjusting screw to set the crankshaft speed within 850-950 rpm.
Remove the clamp from the hose going to the idle air control valve. Connect the crankcase ventilation hose to the cylinder head cover.
Connect the gas analyzer according to the operating instructions.
Make sure that the engine idle speed is within the specified limits.
Turn on the high beam headlights.
Measure the CO content in the exhaust gases, which should be within 0.5-1.5%. If it deviates from the norm, remove the plug of the mixture quality adjustment screw. Using a socket wrench with an internal recess for a 3 mm key, turn the adjustment screw until the specified CO value is obtained. When turning the screw clockwise, the CO content increases and vice versa.
Note: The electric cooling fan should not turn on during idle speed adjustment.
[The original article is available on the website «AudiManual»]