Idle Mixture Adjustment Procedures

1. Before checking or adjusting fuel mixture:
a. Engine should be at full operating temperature (cooling fan cycles at least once and oil temperature is 80°C (176°F).
b. Ensure all electrical loads are disconnected.
c. Ensure exhaust system is in good condition.
d. Ensure ignition timing is set to specifications.
e. Disconnect crankcase breather hose and vent to atmosphere.
2. Connect a duty cycle meter (VW 1367 or Siemens 451 or equivalent) to two terminal test connector.
3. Connect CO tester to exhaust manifold sampling tube.

Fig. 7 Differential Pressure Regulator Test Setup:

4. Connect test harness (VW 1315) Fig. 7, to the differential pressure regulator.
5. Connect a digital multimeter to the test harness. Ensure multimeter is set for 20 mA.
6. Start engine and observe mA and CO readings.
CO should be -- 0.3 - 1.2%
Current reading should be -- 4 - 16 mA, and fluctuate slightly.
7. If CO reading exceeds 1.2% with a reading of 4 - 16 mA, check:
a. Ignition timing
b. Exhaust system for leaks
c. Fuel distributor for even fuel distribution
d. Injector inserts for leaks as follows:
1. Pull the injectors out of the inserts (leaving the fuel lines attached).
2. Using a 13mm allen wrench, remove inserts (upper and lower parts), and seals from the head.
3. Clean the threads of the injector inserts and the head.
4. Replace the 2 'O' rings, and the bottom sealing washer of each insert.
5. Seal the threads of the upper injector inserts with suitable sealing compound and torque to 20 Nm (14.7 ft. lbs).
6. Install injectors back into the holders.
8. If current reading is not within specification, then adjust CO with a 3 mm allen wrench (tool P 377 or equivalent) to obtain a current reading of 8 - 12 mA. After each adjustment, remove tool, then accelerate engine briefly to stabilize adjustment before reading mA or CO%.
Turn screw clockwise to lower current reading ,
Counterclockwise to raise current reading.
CAUTION: While adjusting, do not push tool down. Do not accelerate engine with tool in place. .
9. Connect crankcase breather hose. If CO and mA readings change significantly after connecting breather hose, an oil change may be necessary.
10. Turn ignition Off, then install replacement concealment plug.
11. Remove testing equipment.