Vt V6 hissing sound under light throttle

[muso]

After replacing a broken left exhaust manifold stud and cleaning the throttle body I found that there was a hissing sound (like a pod filter but a bit quieter) under light to medium throttle, but it goes away under heavy or fully open throttle.

It has to be something I did :whistling because the sound was not there before I completed the work.
All I did was remove the throttle body intake tube and disconnect the sensor (EGR outlet pipe) on the left exhaust manifold in order to allow enough movement of the manifold to access the broken stud. Everything went well and went back together with no dramas, I find no evidence of a vacuum line being accidently bumped and disconnected nor can I find any split vacuum lines so I am buggered if I know what it is.

The performance is about the same as is the fuel consumption, I am happy to have got rid of the annoying ticking sound caused by the broken manifold stud but I'd love to know what this hissing\sucking sound is under light throttle:bang: Any ideas would be appreciated

 

[accentstencil]

Could be the purge hose has come loose or broken, that happens a lot. It's the elbow shaped hose on the bottom of the throttle body. It might be something else though because I think the car will run worse with the purge hose off.

 

[muso]

Someone did suggest to me that it could be the purge valve but I don't understand how what I did would cause that, but there is one thing I did, I sprayed some Nulon throttle body cleaner into the throttle body butterfly and started the engine (as per instructions on the can) without the throttle body to air cleaner tube, it didn't start but made some strange noises, doing that may have upset something, perhaps I should have put the tube back on first

 

[don0xer]

Got the exact same problem, light coasting accelleration but it goes away when u accel hard. I thought it might have been the new K&N filter but who knows :/ im pretty sure its not the purge hose on the t/b but i could be wrong :/

 

[Not_An_Abba_Fan]

Purge hose is a common problem. Check it first.

 

[robbo10]

Can you only hear this noise whilst the bonnet is up and your in or around the motor. Or is it louder when your sitting in the driver's seat, or much louder if you get out of the driver's seat and then stick your head in under the dash near the brake pedal. If it's coming from under the dash, you might need to change your brake booster because the diaphragm has been damaged or sprung a leak. It does happen, and if it's only a small leak you won't notice the difference with your brakes.

 

[muso]

Yes you can hear it under the bonnet when you quickly 'blip' the throttle on then off again putting it momentarily under load, the sucking sound comes from the back (firewall side) of the throttle body.

I really should remove that engine cover and try listening again with the intake tube connected, maybe then I'll locate it, it may be a split hose or something to do with the EGR valve which I had to disconnect from the left exhaust manifold pipe.

 

[Vt-Brrrlina]

Id agree check the purge hose- has the same thing when my engine was rebuilt - the dude forgot to put it back on - and i had the hissing noise under light load abnd was chewing a bit of extra fuel too

 

[vt_on_20s]

mine has this problem aswell it started happening after i put my k/n filter and cold air intake on so i thought i did something but i didnt go near the t/b.. i checked the purge hose and it looks fine... it sounds sh?t and everyone is asking what the hell is wrong with your car...

 

[don0xer]

My purge hose looks fine, the connections are tightly on. Can they get slight cracks in the hose overtime and cause the hissing that way ?