Sounds like a vacuum leak....

[RaceDiagnostics]

I took the car out of hibernation today and noticed an odd sound when blipping the throttle from outside of the car, not noticeable inside.

No error codes showing, you can only hear it with a sharp/hard blip of the throttle, ie high vacuum.

Any thoughts, sounds like its coming from around the throttle body. I think I will have to dig out my smoke machine.

I'll also get Kim to blip the throttle so I can get closer to try to find the source, a bit tricky from behind the door.

 

[voipio]

The highest vacuum will be during the overrun. When the throttle is pressed down from idle, the manifold pressure, which will be low but not high vacuum, will collapse as the throttle is opened. Maybe it's that inrush of air that is forming the "hiss" that can be heard. Check the air-tightness of the air filter assembly, and airways from there to the throttle.

 

[mike 109444]

Try the old trick of a length of tube into your ear and the other end held near suspect area. Will have the affect of acting as a stethoscope.

 

[ajlelectronics]

You can also spray some brake cleaner. A change in the engine speed will show up an air leak as the extra fuel is sucked in.

 

[RaceDiagnostics]

The highest vacuum will be during the overrun. When the throttle is pressed down from idle, the manifold pressure, which will be low but not high vacuum, will collapse as the throttle is opened. Maybe it's that inrush of air that is forming the "hiss" that can be heard. Check the air-tightness of the air filter assembly, and airways from there to the throttle.

Yes, I "miss wrote", when i blip the throttle the intake pipe is exposed to the high vacuum, it almost sounds like there is a crack in intake pipe.

 

[RaceDiagnostics]

Try the old trick of a length of tube into your ear and the other end held near suspect area. Will have the affect of acting as a stethoscope.

I have a stethoscope and will try that when i get my wife to blip the throttle, its fly by wire so I cant blip it by hand at the throttle body.

 

[RaceDiagnostics]

You can also spray some brake cleaner. A change in the engine speed will show up an air leak as the extra fuel is sucked in.

I was trying that from where I was standing without much success, will try to persuade my helper to come out to the garage tonight.

 

[roofman]

Reverse engineer and spray brake/clutch cleaner around the intake area on idle...never fails to find a vacuum leak

 

[Parm]

Reverse engineer and spray brake/clutch cleaner around the intake area on idle...never fails to find a vacuum leak

Like your new avatar and statement

 

[roofman]

Like your new avatar and statement

cheers

 

[RaceDiagnostics]

Ok, I'm now thinking that its actually noise from the gears in the throttle body, perhaps its always been like that or maybe its getting worse.