Got an odd one for you...

Since I got it over 2 years ago, my car whistles from around the throttle body on light acceleration from 2000-4000rpm. There is no vacuum leak (confirmed by attaching a gauge to one of the vacuum hoses on engine side of throttle body and also, (with the engine off), the hissing sound of air when one of the vacuum tubes is disconnected after the car has been sitting overnight).

The whistle goes if I apply full throttle. I can even hear it when I open the engine cover and blip the throttle just lightly. I cleaned out the idle control valve today, but the whistle is still there. I have checked all the engine breather hoses & sprayed carb cleaner around every joint in the induction system repeatedly, with no effect on the idle speed, so I don't think this is an induction/vacuum leak. I even took my motorsound cover off & put the original one on, but no improvement.

Seems that a few cars have this problem going by what I've seen on the internet forums... a whistling throttle body.

Has anyone found a solution? It's driving me mad.

By the way, my car's a 1994 normally-aspirated non-varioram, 107,000 miles & drives beautifully otherwise.

Thanks,
Roddy (UK)

 

I'm a little confused about your test for an intake leak. It sounds like you tested the vacuum system, which is totally different from testing for leaks in your intake. Two different systems, two different tests. To test the intake, you're supposed to pressurize the whole intake by removing the airbox (& MAF too i think) then bolting up a plate with an air fitting & pressurizing it.

I found that 3 of the 4 screws holding my throttle body in place had fallen out! Big leak. But the vacuum system seemed fine.

The leak test for the intake is described in the workshop manuals (but trust me, it's not informative at all). I think I saw the leak test for the vacuum system described in a TSB and it specifies how well the pressure should be held (the intake leak test doesn't specify how well the pressure should be held, probably because it leaks pretty bad around the shaft of the resonance flap).

 

Interesting thanks. I guess you couldn't pressurise the intake side easily because air would flow down the engine breather hoses too? I'll check the workshop manual as you suggest.

I wonder if I do indeed have an air intake side leak. Question is where? Will check that all of the throttle body screws are in situ & tight!

If I had a leak on the induction side though, would my extensive spraying with carb cleaner spray all over the joints & pipes not have made the idle speed rise?

Thanks
Roddy

 

How about the crankcase breather cover & hose? It's directly behind the throttle body, on top of the case.


Andreas

 

This happens with carbs when the throttle blade shaft to body clearance is excessive. Air must get draw in through the clearance causing the whistle. You probably just don't hear it at higher engine rpms. I'm not familiar with the Porsche throttle body. Could it have a similar problem?

 

Maybe you have a supercharger and never realized it

All kidding aside, BOL with your search!

 

Funnily enough it does sound like a turbo spooling up.

Been out & check crankcase breather cover & hose. Look ok but will spray with carb cleaner & see if idle speed rises.

Any other ideas?

 

Roddy,

this post is pretty old, but did you ever find out what the issue was, I am experiencing the same symptoms on my 95 non-varioram

 

There is a resonance tuning flap inside the lower chamber of the air distribution plenum. The flap rotates on a shaft that penetrates the plenum housing (wow, that sounds dirty!). I've always been suspicious about how well this point is sealed, because I always find some oil residue around this area. This seems like a potential source of a minor air leak that might cause a whistling sound.

 

HAH! Thanks! That would make sense. I do know the spot where you are talking about. Do you know if there is a reseal kit for this shaft?

 

I looked at the PET, it appears that the entire unit is the only thing available. I've not been concerned enough to disassemble the whole thing, to see if there is a replaceable seal. Hopefully, someone reading this thread has already been there and done that...