Volkswagen Golf/Jetta 2 manual

Idle mixture - adjustment
Fuel and exhaust systems - K-Jetronic fuel injection - 8 valve engines / Idle mixture - adjustment

Note: Accurate idle mixture adjustment can only be made using an exhaust gas analyser 1 The idle CO adjustment screw alters the height of the fuel metering distributor plunger relative to the air control plate of the air flow meter.

2 The screw is accessible by removing the locking plug from between the air duct scoop and the fuel metering distributor on the airflow meter casing (see illustration).

7.2 Idle CO adjustment screw location (arrowed)
7.2 Idle CO adjustment screw location (arrowed)

3 Although a special tool is recommended for this adjustment, it can be made using a long, thin screwdriver.

4 Ensure that the engine is running under the same conditions as those necessary for adjusting the idling speed and that the idling speed is correct.

5 Connect an exhaust gas analyser to the tailpipe, as directed by the equipment manufacturer, and read the CO level.

6 Turn the adjusting screw clockwise to raise the percentage of CO and anti-clockwise to lower it. It is important that the adjustment is made without pressing down on the adjusting screw, because this will move the airflow sensor plate and affect the adjustment.

7 Remove the tool, accelerate the engine briefly and re-check. If the tool is not removed before the engine is accelerated, there is a danger of the tool becoming jammed and getting bent.

8 Recheck that the idle speed is correct and further adjust if necessary.

9 When reconnection of the crankcase ventilation hose results in an increase in the CO content, the engine oil is diluted with fuel and should be renewed. Alternatively, if an oil change is not due, a long fast drive will reduce the amount of fuel in the oil.

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