Low Altitude Adjustment (Below 1000 Meters/3280 FT.)

NOTE: Until 2/88 the throttle bypass screw in the throttle housing was installed in a fully seated position and was not used for adjusting the idle speed. Beginning in 3/88 the throttle bypass screw was no longer installed.

Check first:
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.

1. Remove the cap from the charcoal canister (located near the coolant reservoir).
2. Remove and plug the crankcase breather hose.

Harness Adapter For Checking Differential Pressure Regulator Current:

Checking Differential Pressure Regulator Current:

3. Install a test harness (VW 1315 A/1 or equivalent) between the differential pressure regulator and its harness plug.
4. Connect a multi-meter to the test harness and set it to the 200 mA scale.
5. Remove the cap from the exhaust sampling tube and connect an exhaust gas analizer.
6. Start the engine and let it idle.

The meter values are:
Differential Pressure Regulator current (oxygen sensor connected);
Checking ........... 0 +/- 3 mA
Adjusting .......... 0 +/- 1 mA
CO volume ........ 0.3 - 1.2%
7. Adjust the mixture by drilling a hole in the mixture adjustment concealment plug (located on the air flow sensor housing between the fuel distributor head and the intake air boot), and using a sheet metal screw and pliers to extract it.
8. With the engine running, and the oxygen sensor connected, turn the adjustment screw with a 3 mm allen wrench until the mA and CO readings are within specification.