Bart-Jan

I went to get some new front tyres and when I drove away, the engine made a strange loud whistling noise. It appears to come from the back of the engine. Any clues what it can be?

Facts:
- The car is a Euro '85 16V
- Pitch stays almost equal at all revs
- During accelerating fast, the whistling is gone
- It becomes a little louder when decellerating
- After switching the engine off, the sound continues a few milliseconds longer than running of the engine.
- I removed the airpump and sealed the outlets/inlets on the heads with nuts with some plates welded on top to close the openings. To prevent any air going in/out, I added some rubber seals made from old innertubes.
- The inlet system is standard, appart from a completely inside opened airmeter, because it was of no use to me, because of the step to Megasquirt.

Can the whistling be from the old openings for the airpump? Do the facts correspond with this?

I hope to fix this quickly, as I'm heading to Bockhorn tomorrow for a long weekend strawling between classis cars, parts and motorbikes in the North of Germany. I would like to take my Shark, of course! Thanks in advance for your help.

blown 87

Vacuum leak some where.

WallyP

Get five feet of small rubber or plastic tubing. Crank the engine, stick one end of the tube in your best ear, and use the other end to locate the vacuum leak.

mj1pate

+1

With my 32 valver, I was certain I had an insidious problem that sounded much worse, until the "tube locater" pointed at a rubber coupler between the intake tubes and the central collector. Concentrate on large rubber air passages and you will probably find your problem.

Mrmerlin

.I would look at the blue check valve attached to the small feed line off the booster, it probably need to be replaced or you can try squirting a few drops of silicone spray into it to wet the innards,
best to replace it though, if its making noise

Bart-Jan

Many thanks for your input! I will try your options tonight!

killav

My car did this and it was a collapsed vacume line going to the blue check valve by the brake booster. The vacume line (which I had recently replaced) was being sucked closed because the rubber was to thin.

Bruno Kuzmin

Hello,

I have also whistling problem. When I start cold engine it runs at the beginning normally. After around 20 seconds it stars whistling. What can be a cause?
Here is the link to video, whistling starts at the end of the video

928NOOBIE

I have an '86 but have not heard a leak like yours; it's interesting that all of a sudden it sounds like something "pops" . Check all the clamps for all rubber boots...one or more could need tightening...you'd be surprised how tight they need to be to support the amount of vacuum needed. You could have a bad connection at the ICV.

Crumpler

Also, look at intake manifold gaskets. A common issue for the S3. Nice intake refresh BTW.

Bruno Kuzmin

Gaskets looks OK. It is strange that whistling is not present at start of cold engine. Whistling starts after some time, today it was after 2 minutes of running. And yes, it sound like something "pops" and opens something.

Tomkat80222

Does it start whistling if you allow the car to just idle? Or does it happen, like in the video, after you increased the RPM's?

Jason89s4

+1 on checking connections and hoses to Idle Stabilization Valve (ISV).
-Jason

rjtw

Sounds to me like it happens when the accelerator is suddenly released, causing a big increase in vacuum (or big decrease in pressure, you pick). As a pointless experiment you could just let the engine idle without touching the accelerator, and if no whistle after several minutes then induce it by revving up the engine and -suddenly- releasing the accelerator.

My money would be on a vacuum line somewhere that partially collapses under "too much" vacuum and then can't rebound. Or potentially a partially failed one-way valve if those have a similar failure mode.

Anyway, OP, you have a bunch of great suggestions in this thread and a method by which you can listen and figure things out -- up to you now! Good luck and let us know how it goes.

And PS -- yeah, nice intake!!

Geo55

What happened with the OP's vacuum leak search??