Vacuum Advance, Checking

Vacuum advance, checking

- Connect VAG 1368 tester or equivalent according to manufacturer's instructions.
- Connect vacuum tester between throttle valve housing and vacuum advance unit connection.
- Set vacuum tester to allow vacuum to pass through.
- Pull off hose from vacuum retard unit.
- Disconnect plugs from idle stabilizer control unit and connect together.
- Start engine and adjust idle speed to 900 RPM.


Checking with TDC sensor:
- note advance angle on tester (basic advance angle).

Checking with timing light:
- Shine timing light on ignition timing scale and note indicated angle (basic angle).
- Increase engine speed until reading on vacuum tester is higher than 360 mbar (270 mm Hg)
- Switch vacuum tester so that it holds vacuum on side connected to vacuum unit.
- Leave engine running at idle: 900 RPM
- Reduce vacuum on vacuum tester to 360 mbar (270 mm Hg) or 190-230 mbar (140-170 mm Hg).
- Note advance angles.
- Determine vacuum advance by subtracting basic advance angle from measured advance angle

Example
Last advance angle measured (-) minus basic advance angle (=) vacuum advance

- Compare vacuum advance angles with specified values on specification chart.
- Readjust idle speed.