FredR

If the passive vac system fails you lose the ability to change the position of the flappy from 3600 to 5200 [or whatever the change over it is. That does not impact the bottom end, rather the business end of the plot loses 50 plus HP.

If the O2 sensor and cats were removed then logically the coding plug needed to be changed and the car would need the resistance pot to fine tune the tick over mix. If you do not have these then I wonder how things are being controlled? I have no idea why you would want to go to W8 plugs but if there is a need then something seems to be not quite right here.

Rgds

Fred

kos_007

Diagnosing a vacuum leak could be frustrating. You need a plan of action, patience, MightyVac and proceed methodically. First, test if the vacuum line themselves. The static vacuum system with it's 4-way splitter under the brake booster also supplies vacuum to the climate control flap actuators via the vacuum solenoids - with the ignition ON and vacuum applied you can cycle the lower slider on the HVAC head unit - you will see a small drop in vacuum every time you activate a new flap, but the system still should be able to hold vacuum. Other connections to the static vacuum system are the "vacuum accumulator" and vacuum supply to the flappy valve which runs via a solenoid in front of the left cylinder bank. The "dynamic" vacuum system is supplied by the vacuum line originating in the throttle body and it supplies vacuum to 2 fuel pressure dampeners, FPR and the transmission (AT) via the 5-way splitter in the back, under the MAF. Then it goes the intake manifold itself with a myriad of hoses, gaskets, rubber boots etc. Frequently overlooked items are the lower fuel injector seals and the needle bearings for the throttle and flappy valve. In this case a smoke machine is your best friend - some shops have them or you can make your own - check youtube. Good luck with the project. Tony.

kos_007

Oh, forgot to mention that the static vacuum system also controls the water valve for the heater - the vacuum line from the climate control solenoid bank behind the center console runs back to the engine compartment to the heater valve actuator - may cause hiss if disconnected or the rubber elbow cracked.

mark kibort

is this normal, or what could be making this sound... its actually less here than normal, but you get the idea

NZ928S4

This is exactly the sound mine makes. At part throttle it goes away. But at idle or low speed theres this sound just like the one in the video above.

Really annoying...

Tried the dipstick, oil filler no change. Anybody got a solution as Mark has the same issue?

Do all S4's do this?

harveyf

I listened to Mark's video. If pulling the dipstick doesn't affect the tone of the noise, I would suggest looking for a moving part that is rubbing versus a vacuum leak. Prime candiate are the pulley's on the front of the engine. A lesser candidate would be the rotors inside the distributor housing. For that matter, any of the idler bearings on the cam belt drive might cause such a noise. Get out your mechanics stethescope (or a rubber hose) and try and isolate where the noise is coming from.

mark kibort

it is absolutely a air noise in the intake. there are no leaks. it's whistling through the maf or something resonating in the intake
it is a high pitched air whistle noise.
by the way, ive disconnected and plugged all vacuum lines. actually left one open accidentally for a while and you could never hear any effects. this is a high volume flow air sound, not some small vacuum leak

Mrmerlin

get the Myty vac and connect it to the flappy line,
open the flappy see if the noise goes away,
if so then maybe the nut stop for the flappy arm is opened a bit more .

Otherwise get a long piece of rubber or silicone tubing stick one end in your ear and put the other end around and listen for the noise and where it is loudest

NZ928S4

Mark, I agree "it resonates" is the correct sound. Putting pressure on the right rear side of the intake plenum sharply reduces the sound. You can feel in the palm of your hand. At part throttle it goes away.

Since I just had the intalke manifold off and went trhough everything .This to change the flappy because the f*ing hose connector came off under the manifold . Change the flappy vacuum controller while I was there as existing one worked but after 22 years why not?

Engine made exactly the same sound before and after all the work. Intake gaskets and rubber seals.changes, new gaskets on the portion you remove to get at the flappy controller.

Wrapped the plenum with electrical tape as a test even though I had re cemented gasket and plenum before taking intake off. Just too see if it leaked around the seam. No difference.

Is this a normal sound on all S4'S?????

Chalkboss

I have the whistle at idle on my 87. Did a complete intake refresh, everything new. Made the same whistle before. No leaks that I know of. Interested to hear what other S4 owners say.

mark kibort

I have removed the flappy, and this noise just appeared over the last two years.
my take on it, is that the whistle is something happening around the MAF sensor . taking the airbox off and starting the engine makes it worse.

kevin2012

I have the same whistle noise in my 91S4 engine too. I agree that it is like an air related noise. Everything seems fine. I have this noise from day one when I purchased this car.
I like to get rid of it too.
Cheers.

NZ928S4

Hmm surprised nobody has a fix for this? Or has figured out how to stop. Wrapping the whole manifold with duct tape is an interesting but not a permanent fix. After putting on about 4 layers of paint on the manifold had to believe a pin hole leak.

mark kibort

I dont think its a leak... im thnkng its a flow disturbance in the MAF , but nothng has changed there , so its reallly puzzling. a leak, would tend to make the idle rise and it doesnt. in fact, i can open the vacum lines and there is no sound from that kind of leak. althougth, that wistle, makes me think that there is a vacuuum port on the TB (behind the throttle plate) that might be leaking or disconnected.
time to recheck vacuum. those little ports might make a perfect whistle.

merchauser

Its been some time since anyone has posted about this whistle....has anyone found a solution?