INTAKE MANIFOLD FLAP
Intake Manifold Flap.
This is not the same as intake manifold runner flap
What does it do ?
The intake manifold flap closes when stopping the engine. This reduces shake or shudder and so it is sometimes called an anti-shudder flap. The engine stops quicker because the flap has blocked the air supply to the intake.
The flap is built into the EGR valve housing.
How does it go wrong ?
If it fails in the open position you may not notice. The engine will run fine but may shake a bit more than usual when you switch off.
If it fails in the closed position the engine will not start as it isn’t getting any air.
What makes it go wrong.
On the B5 passat and similar 1.9 tdi engines the intake manifold flap is sprung open so should stay open when the engine is running. When the engine stops, the N239 solenoid valve applies vacuum and the flap closes for 3 seconds. This is enough to stop the engine shuddering. The flap then springs open again.
Causes of failure.
1. Vacuum pump failed. This will be obvious as other systems won’t work properly. (Including brakes)
2. Vacuum pipes damaged/leaking. Check vacuum pipes for damage
3. N239 valve failed. Turn ignition on, pull the vacuum pipe off before the N239 valve, pull the vacuum pipe off the manifold flap actuator and blow down the first pipe. If you can't blow, repeat with the ignition off. This will confirm that the N239 is opening the vacuum pipe and so should be closing the flap.
N239 failure results in the manifold flap staying open and not shutting when you switch off.
4. Actuator failed. Disconnect the vacuum pipe at the actuator and suck. If you find you are sucking air (like through a straw) the actuator is no good.
5. Jammed manifold flap. When you suck you should move the flap. If it doesn’t the flap is jammed.
You can try cleaning the manifold flap. If this doesn’t work you will have to replace the EGR complete.
A failed (open) Intake manifold flap may flag a fault code rather than show up as a problem.
Valve for Intake Manifold Flap (N239), Short to B+
Valve for Intake Manifold Flap (N239), Short to Ground
A failed (closed) Intake manifold flap may flag a fault code but as the engine won’t start, it will be obvious you have a fault.
On the B6 the vacuum system has been replaced. The actuator is an electric motor (V157) driven by a wire from the ECU. (No vacuum pipes needed). Failure symptoms are the same as a B5.
Causes of failure.
1. It won’t be vacuum so don’t touch the pipes.
2. The wire from ECU to manifold flap motor (V157) could be damaged. (Short to +, short to earth or open circuit). This should flag a fault code.
3. The manifold flap motor (V157) may have failed. This will give the same codes as a damaged wire.
4. The flap may have stuck. This nearly always breaks the actuator motor levers.
The result of any of these is that the flap is either, open, closed or stuck part way.
Motor damage or wire short to earth will blow the fuse. When this happens the radiator fan stops working because it’s on the same circuit.
5. Finally a damaged radiator fan can blow the fuse and stop the intake manifold flap working. ALWAYS CHECK THE FUSE.