Intake Manifold Change-Over, Checking

Intake Manifold Change-Over, Checking
This test should only be performed if there is a performance deficiency.

The intake manifold switches from the long intake path to the short one at approx. 4500 RPM.

Special tools and equipment







- VAG1390 Hand Vacuum Pump

Checking function
- Start engine and let run at idle.

The actuator (vacuum diaphragm) at intake manifold holds the change-over shaft in the long intake path position.
- Have a 2nd person briefly depress the accelerator pedal (acceleration burst). Observe the actuator during this (installed position: at intake manifold on right).







- Actuator must operate the change-over shaft in the intake manifold (arrow).

If the actuator does not generate the change-over motion:
- Switch ignition off.
- First, test the activation of the intake manifold change-over valve -N156- via output Diagnostic Test Mode (DTM). [1][2][3]Output Diagnostic Test Mode (DTM) (Function 03)

If activation is OK:







- Disconnect vacuum hose -1- at check valve -2-.
- Connect VAG1390 hand vacuum pump to vacuum hose -1-.


NOTE: Output Diagnostic Test Mode (DTM) is switched off after 1 minute. If it is necessary to repeat output Diagnostic Test Mode (DTM), the engine must be started and run briefly.







- Perform output Diagnostic Test Mode (DTM) again. When the intake manifold change-over valve is activated, operate hand vacuum pump evenly. The setting element must oscillate back and forth between the two positions.

If the change-over does not function as described:
- Check whether the change-over mechanism moves easily. Unclip linkage from change-over shaft and operate change-over shaft by hand.
- Check whether the vacuum lines are correctly connected.
- Also check the vacuum system including the vacuum reservoir.


NOTE: The vacuum reservoir is bolted on behind the cylinder head above the exhaust manifold heat shield.