Audi Workshop Service and Repair Manuals

This test should only be carried out if the engine is losing power.

The operation of the intake manifold change-over valve is dependent on the engine load and engine speed.

Testing function

• ‒ Run engine at idling speed for 2 or 3 minutes (to build up a vacuum which is required to operate the intake manifold change-over function).

• ‒ With engine not running and ignition switched on, start final control diagnosis and select intake manifold change-over valve -N156
  =>Page 01-55.

→ The vacuum unit for the intake manifold change-over valve should pull and release alternately (until vacuum supply in integral vacuum reservoir is used up). When the engine is not running, the vacuum is sufficient for approx. 4 change-overs. Location of vacuum unit (vacuum actuator):=>Page 24-92 )

If the change-over is not taking place, carry out the following tests:

• ‒ Test intake manifold change-over valve -N156 (perform final control diagnosis=>Page 24-90).
• ‒ Make sure that vacuum hoses are properly connected and free of blockages and leaks.
• ‒ Make sure that change-over mechanism can move freely (actuate linkage by hand).

Testing vacuum system

• ‒ Run engine at idling speed for 2 or 3 minutes (to build up a vacuum which is required to operate the intake manifold change-over function).

Note:

The vacuum reservoir is part of the intake manifold and cannot be renewed separately.

• ‒ Switch off ignition.
• ‒ Unplug 2-pin connector from intake manifold change-over valve.

• ‒ → Connect one of the contacts on solenoid valve to engine earth using test cable and crocodile clamp from V.A.G 1594.
• ‒ Connect second contact on solenoid valve to positive via remote control V.A.G 1348/3A using adapter lead V.A.G 1348/3-2 and auxiliary cable.
• ‒ Operate remote control V.A.G 1348/3A for 2 or 3 minutes. During this time the vacuum unit should remain in the pulled-in position.

If the vacuum unit returns to rest position, test the vacuum unit as follows:

• ‒ Disconnect vacuum hoses from vacuum unit for intake manifold change-over valve.
• ‒ Connect hand pump V.A.G 1390 to vacuum unit.

• ‒ Operate hand pump and observe change-over action.
• ‒ Test vacuum unit for leaks. (The vacuum unit should not return to rest position until the hand pump is vented to atmosphere.)
• ‒ If necessary, fit a new vacuum unit.

• ‒ If the vacuum unit does not pull, check to ensure clear passage through -N156 as follows:
• ‒ → Connect one of the contacts on -N156 to engine earth using test cables and crocodile clamp from V.A.G 1594.
• ‒ Connect second contact on -N156 to positive via remote control V.A.G 1348/3A using adapter lead V.A.G 1348/3-2 and auxiliary cable.
• ‒ Operate remote control V.A.G 1348/3A.
• ‒ Check to ensure clear passage through valve (disconnect vacuum hoses and blow through).
• ‒ If necessary, fit a new intake manifold change-over valve.