Air Flow Sensor Potentiometer

NOTE: Do not remove the potentiometer from the air flow sensor housing for any testing or inspection purposes. On the CIS-E III injection systems, the air flow sensor potentiometer is not a replaceable component. Unlike earlier CIS-E systems, if the potentiometer is found to be faulty, the complete air flow sensor housing must be replaced.
1. Initial setup
a. Engine must be at normal operating temp (80°C/176°F).
b. Fault code display has been initiated.
c. Valve cover must be tight, and gasket in good condition.
d. Oil dipstick must be sealed completely.
e. All electrical consumers (including A/C) must be switched OFF.
f. Ignition timing must be correctly set.
g. Idle mixture must be set to specification.
2. To gain access to the potentiometer harness plug,
a. Remove the air duct to the oil cooler,
b. Air filter housing from its lower bracket.
c. Disconnect the upper air filter housing and push the air flow sensor assembly away from the fender.
3. Test the resistance between terminal 3 of the harness plug and ground. Resistance should be less than 0.8 ohms.
4. If resistance is not within specification, repair wiring.
5. Check the voltage between terminals 1 and 3 of the harness plug. With the ignition ON, the potentiometer supply voltage should be 4.35 - 5.35vdc. Note the exact voltage.
6. If voltage is not within specification, check wiring between the potentiometer harness plug and the injection control unit plug. Pin designations are:

Potentiometer Plug Control unit plug
1 ...................................... 26
2 ...................................... 23

Resistance should be less than 0.8 ohms. Repair wiring as necessary.

Fig. 8 Test Harness VW 1501:

8. Connect test harness VW 1501, Fig. 8, between the potentiometer and the harness plug.
9. Connect a voltmeter to terminals 2 and 3 of the test harness.
10. With the ignition ON, and the sensor plate in the REST position, output voltage should be 0 - 200 mV.
11. To stabilize ignition timing for the test, insert the spare fuse into the fuel pump relay (do not remove until test is completed). Idle speed should change slightly.
a. With the engine running at idle, remove the harness plug from the Idle Control Valve. The engine speed must increase.
b. Clamp one of the hoses from the idle control valve until engine speed decreases to 780 - 820 rpm. Ignition timing should be 13 - 17° BTDC, adjust if necessary.
c. Connect voltmeter to terminals 2 and 3 of the test harness, and note output voltage reading.

Fig. 16 Air Flow Meter Potentiometer Voltage Value Graph:

d. Compare output voltage to supply voltage, noted in step 5, according to graph in Fig. 16.
e. If the output voltage is only slightly below the specified values, check for air leaks in:
1. Intake air boot
2. Crankcase ventilation hoses
3. Charcoal canister hoses
4. Vacuum lines
f. If the system has no leaks, see "AIR FLOW SENSOR POTENTIOMETER" in "ADJUSTMENT PROCEDURES.".