Porsche 964 intake resonance flap rattle

[nrg250]

Dear all, re my 964 c4 coupe, manual, 1992, 150k miles, plastic intake manifolds, (runs well bar a little hesitation at low revs), but there is a rattle from the top of the engine coming from the actuator that controls the resonance flap. If I reach in and hold the rod from the actuator, the noise goes away. I can also move this rod by hand, so it is not held firmly in either the open or closed position but it is connected.
There is a characteristic "click" when I turn the ignition on, but it's not coming from the actuator which doesn't move when the ignition is turned on.

My questions is - do these actuators fail, or do the flaps inside the intake fail?

Has anyone had this issue before, and is there a good way to verify where the problem is before stripping the intake off the engine?

Thanks very much

[Slippydiff]

nrg250 said:

Dear all, re my 964 c4 coupe, manual, 1992, 150k miles, plastic intake manifolds, (runs well bar a little hesitation at low revs), but there is a rattle from the top of the engine coming from the actuator that controls the resonance flap. If I reach in and hold the rod from the actuator, the noise goes away. I can also move this rod by hand, so it is not held firmly in either the open or closed position but it is connected.
There is a characteristic "click" when I turn the ignition on, but it's not coming from the actuator which doesn't move when the ignition is turned on.

My questions is - do these actuators fail, or do the flaps inside the intake fail?

Has anyone had this issue before, and is there a good way to verify where the problem is before stripping the intake off the engine?

Thanks very much

Yes they do (the diaphragm fails) and it leads to some pretty chunky hp and torque losses.
They can be tested with a small hand held vacuum pump which has a gauge that enables you to establish if the valve diaphragm is holding vacuum.

HTH.

[nrg250]

that's great thank you

[Slippydiff]

This kit is about as cheap as it gets. Though to quote Gerald Ratner, "an M&S sandwich will probably last longer ..."

Ebay link : https://tinyurl.com/cd848ne

but it should enable you to test the diaphragm easily.

[nrg250]

Thats really helpful, thank you

[nrg250]

Thats really helpful, thank you