Diagnostic Strategies

CHECKING ALL ENGINES EXCEPT 1984 4 CYLINDER
- Engine oil temperature minimum 80°C (176°F)
- All electrical consumers switched off
- Oxygen sensor connected
- Remove cap from CO probe receptacle
- Connect CO tester
Hose must fit snugly so that there is no exhaust leak
- Remove wiring connector from differential pressure regulator
- Connect adapter VW 1315 All and multimeter US 1119
Set multi meter to 200 mA scale
- Connect engine tester to test plug using adapter US 1112 and set tester to 4 cylinder scale

NOTE: Only connect the (+) and (-) and (dwell) leads of VW 1367 or Siemens 451. If other test leads are connected the "duty cycle" readings for the idle air stabilization valve will be inaccurate.

- Start engine
- Check duty cycle of idle air stabilization valve 28% +/- 2% (23° - 37°)
- Shut off engine





- Reconnect engine tester to make idle RPM and ignition timing checks
- Start engine
- Check idle RPM:
850 +/- 50 RPM for 1985 and 1986 M.Y. 4 and 5 cylinder engines
- Check ignition timing: 6 + +/- 2 + BTDC
- Check CO%: 0.3% to 1.2%
- Check differential pressure regulator current (4 cylinder engines) 10 mA +/- 6mA (5 cylinder engines) refer to graph below
- If all values are within specifications shut off engine and continue with fuel system pressure checks
- If all values are not within specifications, continue with adjusting procedure





ADJUSTING ALL ENGINES
- Remove cap from carbon canister purge line
- Disconnect crankcase breather hose and vent to atmosphere

NOTE: On 5 cylinder engines, disconnect both crankcase breather hoses from valve cover and plug both T connections at valve cover.

- Connect engine tester using adapter US 1112 and 4 cylinder scale.
- Start engine
- Adjust duty cycle of idle air stabilization valve to: 28% +/- 1% (25 +/- 1°) RPM should be 850 +/- 50 RPM for 1985 and 1986 M.Y. 4 and 5 cyl. engines.
- Shut off engine
- Reconnect engine tester to continue with ignition timing and CO% adjustments
- Start engine
- Adjust ignition timing: 6° +/- 1° BTDC
- Adjust CO%: 4 cylinder engines 10 mA +/- 1 mA with oxygen sensor connected. 5 cylinder engines 0.8% +/- 0.2% with oxygen sensor disconnected. Differential pressure regulator current must correspond to graph.

NOTE: Current reading must fluctuate when oxygen sensor is connected. If not, check oxygen sensor system.

If CO% cannot be adjusted to specified range check engine condition (intake leaks, exhaust leaks, etc.)