Volkswagen Golf/Jetta 2 manual

Idle speed and mixture - adjustment
Fuel and exhaust systems - Digijet fuel injection / Idle speed and mixture - adjustment


1 The idle speed can only be accurately checked using a suitable tachometer and an exhaust CO analyser. VW recommend that the inlet air temperature sender in the airflow meter must ideally be set to 1.8 K ohms to provide a neutral air inlet temperature. As this requires the use of specialised VW equipment, an approximate check/setting will therefore have to suffice.

2 When checking or making any adjustments to the idle speed, it is important to adhere to the following:
a) The engine must be at its normal operating temperature
b) All electrical components must be switched off, including the cooling fan c) The ignition timing adjustment must be correct
3 Pull free the crankcase ventilation hose from the pressure regulating valve and plug it.

4 With the ignition switched off, connect a tachometer in accordance with the manufacturerТs instructions, then connect the CO analyser to the measuring pipe (see illustration). An adapter will probably be needed to ensure a good seal between the analyser hose and measuring pipe.

3.4 CO analyser and connecting pipe
3.4 CO analyser and connecting pipe

5 Disconnect the Lambda probe wiring plug from its in-line connector.

6 Start the engine and check that the idle speed and CO content are as specified. If the idle speed is too high, check that the throttle valve is fully closing before making any adjustments to the idle speed.

7 If adjustment to the idle speed and/or the mixture (CO content) is required, turn the appropriate adjuster screw as necessary (see illustration).

3.7 Idle speed (A) and mixture adjustment (B) screws
3.7 Idle speed (A) and mixture adjustment (B) screws

8 If the CO content is to be adjusted, the mixture screwТs tamperproof cap will have to be carefully prised free and a suitable Allen key used to make the adjustment. On models produced from July 1989 on, the idle speed should initially be between 900 to 1000 rpm and the CO content between 1.0 and 1.4%.

When the Lambda probe is reconnected, the idle speed and the CO content should settle down to the specified setting. Fit a new tamperproof cap over the mixture screw on completion.

9 With the idle speed/CO content correct, disconnect the analyser and reconnect the Lambda probe wiring plug.


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