Volkswagen Golf/Jetta 2 manual

Idle speed and mixture (CO content) - adjustment
Fuel and exhaust systems - Digifant fuel injection / Idle speed and mixture (CO content) - adjustment


1 Run the engine until the oil temperature is at least 80°C. This should correspond to normal operating temperature.

2 Switch off all electrical components, including the air conditioning, where fitted.

Note that the radiator fan must be stationary during adjustment.

3 For accurate adjustment, the throttle valve switch and idling stabilisation control valve must be functioning correctly and the ignition timing must be correct.

4 With the engine stopped, connect a tachometer to the engine. Plug one of the exhaust tailpipes and position the probe of an exhaust gas analyser in the remaining pipe.

5 Disconnect the crankcase ventilation hose from the pressure regulating valve on the valve cover and plug the hose.

6 Run the engine at idle speed. After approximately one minute, disconnect the wire from the temperature sender (see illustration) and quickly increase the engine speed to 3000 rpm three times.

2.6 Crankcase ventilation pressure regulating valve (1) and temperature
2.6 Crankcase ventilation pressure regulating valve (1) and temperature sender (2)

7 With the engine idling, check the idle speed and CO content. If necessary, adjust the screws (see illustration). The CO adjustment screw is fitted with a tamperproof plug at the factory. This plug should be prised out before making an adjustment.

2.7 Idle speed adjusting screw (1) and mixture (CO content) adjusting screw
2.7 Idle speed adjusting screw (1) and mixture (CO content) adjusting screw (2)

8 Reconnect the temperature sender wire and again quickly increase the engine speed to 3000 rpm three times. With the engine idling, the idle speed and CO content should be as specified. If necessary, make any small corrections required.

9 Fit a new tamperproof plug.

10 Reconnect the crankcase ventilation hose. Note that if this increases the CO content, do not alter the adjustment. The cause is fuel dilution of the engine oil due to frequent stop/start use. A long fast drive should reduce the CO content to the correct level. Alternatively, an oil change will achieve the same objective.


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