NL V6 3.5 Hissing when stone cold

[keith h]

Is it normal to hear a vacuum hissing "somewhere" in the engine bay, when the cold start fast idle is activated?

I can clearly hear the hissing only from a dead cold start. Fast idle is about 1,500rpm. After a couple of minutes the hissing stops and fast idle is down to about 800rpm.

After the temp gauge is at normal and idle speed is on 700rpm no hissing can be heard.

I can't pin down where it is coming from but I can hear it in the cabin (no radio and windows up)

I've never noticed it before, Is it normal?

[Para Ordnance]

Check your drive belts, I'd say they are causing the noise! Give them a squirt with a lubricating spray while idling, and see if the noise goes!

[psproule]

The idle air bypass can make a bit of noise, but not so loud that you would hear it in the cabin. I would start by checking that all vac and intake hoses are secure.

[pagerow]

You haven't run over a snake have you Keith?

[keith h]

psproule
So the idle air bypass can make a little noise? That's all it is really.

It's only there for a couple of minutes. Driving with light throttle it goes away. Foot completely off the throttle it can be heard.

I'll keep checking for vacuum hoses, but it sounds like it is pretty normal.


Para Ordnance
I don't think it is belts. Throttle position affects it and it is classic vacuum hose off sound.

pagerow
Good idea, but I don't think so.

[psproule]

I used to be able to hear it on our petrol NM. Typical intake sucking sound when it was cold. Couldn't hear it in the cab though.

Pat