Air/Fuel Mixture: Adjustments

Requirements:
Engine at normal operating temperature, 80°C (176°F).
All electrical consumers (A/C, rear window defroster, etc.).
Radiator fan must not be running while checking or adjusting.
No fuel pressure gauges connected to the fuel system.
If the injection lines were loosened or replaced, run the engine up to at least 3000 RPM several times to clear the system of trapped air before making adjustments.
Exhaust system must be tight and free from leaks.
Oxygen sensor system in good working order.

Harness Adapter For Checking Differential Pressure Regulator Current:

Checking Differential Pressure Regulator Current:

1. Connect a test harness (VW 1315 A/1 or equivalent) between the differential pressure regulator and its harness plug.
2. Connect a multi-meter to the test harness.
3. Connect an exhaust gas analyzer to exhaust sampling tube.
4. With the engine at idle, test values should be:
Pressure regulator current ...... 0 - 5 mA (and fluctuating)
CO volume ........................... 0.2 - 1.2%
5. If the current reading does not fluctuate, check the oxygen sensor system.
6. If the CO reading is not within specifications, adjust as follows:
a. Drill a small hole in the CO adjustment hole concealment plug (located on the air flow sensor housing between the fuel distributor and the intake air boot), and use a sheet metal screw to extract it.
b. With the engine at idle, use a 3 mm allen wrench to turn the mixture screw until the CO is within specifications.
c. Turn the screw
Clockwise to increase CO
Counter-clockwise to decrease CO
7. After the system is adjusted, remove all test equipment and install new concealment plug.