VVIS inspection

[bruckner]

My car developed a strange and fairly loud drone like noise at idle after the major 90,000 mile service (which did not include pulling the VVIS assembly to inspect screws, I found out only recently that it was an area of concern), the mechanic who performed the work inspected the alternator and a/c tensioner bearings and found them to be in good shape, he concluded that the noise was coming from the valley of the engine right where the VVIS is.

The drone like noise is heard only at idle and disappears with the slightest increase in RPM never to return before low speed idle resumes.

I will do my own inspection of the screws holding the VVIS plates using a borescope, if only for peace of mind, but I'm speculating that perhaps my VVIS may be stuck open (i.e non functional) and that turbulence resonance or harmonic is produced as a consequence.

I understand that the plates are spring loaded in the open position and vacuum pressure closes them in the 0-4800rpm range. My question is this: is there an easy way to confirm by sight or by feel that the plates close as they should upon startup? I would like to eliminate this possibility before moving to others.

Here is a sound recording of the drone noise: https://youtu.be/I3YUQFXKCbU

 

[Kaz-kzukNA1]

That's easy.

The VVIS linkage mechanism marked in yellow.
The diaphragm marked in blue, operated by the vacuum pressure with the support of vacuum tank inside the control box at the eng bay.

The location of the same linkage on the engine.

How it looks at opened/closed status.

Because of the vacuum tank, if the engine was stopped within the last several hours or even the day before, the VVIS would be in closed position.

If you want to open it up, just remove the #3 vacuum tube as marked here.
That's the one operating the diaphragm in the 1st photo.

You will hear hissing sound as you'll release the vacuum from the tank.
Don't worry.
As soon as you start the engine or even crank it long enough, it will restore the vacuum pressure and immediately closes the VVIS.

Or, you don't even need starting the Eng to close it.
Just use your finger.



Kaz

 

[bruckner]

Kaz, thank you!

The borescope test is really easy to perform and highly recommended to all owners now that these devices are very cheap to buy online. Took me the best of 20 minutes to remove the top of the airbox, run the borescope taking pictures of all 6 flaps, and reinstall everything. Peace of mind could hardly be cheaper.

I've been able to confirm from outside that my VVIS flaps close on startup as they should, so my search for this weird noise continues. I didn't drive the car today but had it idle for about 20 minutes; though quieter than it was when I made the sound file, the noise was still audible after about 10 minutes of running. I suspect it would be louder after an actual drive.

Any ideas?