Checking the Intake Manifold Function

The intake manifold switchover should only be checked if the vehicle does not develop the required power. First, check the linkage and levers manually for free movement. Then perform the function test with the engine at operating temperature.

PROCEDURE

Start the engine and increase the speed above 4000 rpm.

Observe the intake manifold switchover diaphragm unit:
The actuating rod should now move backward.

If this is not the case, check the vacuum hoses for leaks. If they are in order:
Check the diaphragm unit: connect a spare vacuum hose to the unit connection and draw firmly with your mouth.

If the rod does not move and/or a large amount of air is drawn in, the diaphragm unit is faulty. Replace it. If the unit is serviceable:
Check the variable intake manifold switch valve: disconnect both vacuum hoses from the valve. Connect a spare vacuum hose to the intake tube nipple on the valve.

Draw air firmly through the spare vacuum hose with your mouth. Air must not pass (blocked).

Start the engine and increase the speed well above 4000 rpm.

Draw air through the hose with your mouth again. Air must now pass freely (open).

If you still have not located the fault (which in itself is quite unlikely), the control system should be checked by a workshop.

Remove the engine undercover.