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Home >> Audi >> 1998 >> A8 Sedan (4D2) V8-3.7L (AEW) >> Repair and Diagnosis >> Powertrain Management >> Computers and Control Systems >> Testing and Inspection >> Component Tests and General Diagnostics >> Intake Manifold Tuning (IMT) Valve >> Intake Manifold Tuning (IMT) Valve Pneumatic Function, Checking
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Intake Manifold Tuning (IMT) Valve Pneumatic Function, Checking




Intake Manifold Tuning (IMT) Valve Pneumatic Function, Checking

- Disconnect vacuum hose from intake manifold.







- Connect hand vacuum pump VAG1390 to disconnected vacuum hose.
- Operate hand pump at least 50 strokes (build-up of vacuum must be noticeable).
- Disconnect vacuum hose from hand pump.
- The vacuum must be maintained at the IMT valve (decrease between hand pump and check valve only).
- If a release of vacuum can be heard, the check valve is leaking (replace check valve).

- Initiate output Diagnostic Test Mode (DTM) and check actuation of intake manifold change-over (IMT) valve -N156-. Refer to "Scan Tool Testing/Output Diagnostic Test Mode (DTM), (Function 03)" Testing and Inspection


Output Diagnostic Test Mode ->
Intake manifold change-over valve -N156


The valve should click (confirm by sound and touch). The change-over should occur (approx. 2-3 times), but stop when there is no longer vacuum in the reservoir. With no vacuum, the valve will only click. After one minute the DTM will be interrupted.

If no change-over occurs, the following are possible malfunctions:
- Intake manifold change-over mechanism sticking (try moving it by hand).
- Vacuum system leaking (hose connections, lines, reservoir or vacuum unit).
- Check valve (black/white) leaking, plugged or incorrectly installed.
- IMT valve faulty (plugged, or otherwise does not operate).


NOTE: The vacuum reservoir is located under the left-front fender. near the A-pillar.


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