hissing noise

[Timmos]

Gday all.

I've noticed a noise coming from my engine, Sounds exactly the same as if i've taken the airbox out. My car has also been idoling funny latey, will sit at 1500rpm on idol and then randomly drop to 500 and hover between 500 and 1000.

One of my mates suggested something may be blocking the maf sensor. So i took it off and had a look. Nothing seemed to be blocking it. When i started the engine without the MAF sensor, the hissing was 20x louder and i could feel hot air blowing out of the intake. Is this normal?

Oh and i should mension i got a check engine warning today. but the next time i started up it went away. Oh and incase it matters. I'm running LPG. dual fuel system

any ideas?

[Tiger28]

Hi Buddy I put my car on lpg about 2 months ago and what I notice is that sometimes when the car is cold when I start up and drive it makes a sucking noise like hissing ,but when it warms up it goes away.I have been getting check engine light to now sometimes and as like you it goes away.I took it to my Mechanic and he put the computer and plugged in to the bottom of steering to see for any faults and nothing read and all was fine.He then checked the lpg system and said similar nothing wrong.Was told maybe could be O2 sensors but he told me all is fine.Light still comes on now and then.

[Timmos]

Hey mate, cheers for the reply. Only thing i've noticed that's different to yours is mine never goes away. I've had LPG for almost 10,000kms so i'll go for a service and see what i they say i guess

cheers

[batty_123]

ive got lpg dual system on my VY aswell.. but mine doesnt do this?

[whitey66]

Did you check the little rubber vacuum elbow at the bottom of the throttle body?
The plastic hose that goes to the purge solenoid often comes off the rubber elbow and sucks air.
If it has come out,just put some super glue on it and refit it.

[sp001in]

Not sure about the VY but my Vq used to do this. the IACV (Idle Air control Valve) on the throttle body had some dirt in around the seal, and wouldnt always shut properly. Airbox or not the thing sounded like a jet engine, cos it creats a whistle through the airfilter plumbing.

Remove it, clean it with throttle body cleaner and see if it makes a difference.

[Timmos]

Did you check the little rubber vacuum elbow at the bottom of the throttle body?
The plastic hose that goes to the purge solenoid often comes off the rubber elbow and sucks air.
If it has come out,just put some super glue on it and refit it.

Thanks for the comment! but any chance you'd have a pic of this, I'm just not mechanically skilled enough to know what that is :P

sp001in - thanks, i took off the IACV and cleaned it with throttle body cleaner. Definantly looked a bit average. but i've still got the noise. Although my idoling appears to have gotten better!

[Timmos]

Ok, i found the rubber elbow at the bottom of the throttle body and yes the tube that connects to the purge solenoid has come off.
Where is the purge solenoid? I've tried to google it and cannot find a picture of it.

Thanks

[trentvy]

hey mate same problem with mine only the tube that connects to my elbow is only slightly comming off not completely off. whats a good way to get it back on??

[Timmos]

hey mate same problem with mine only the tube that connects to my elbow is only slightly comming off not completely off. whats a good way to get it back on??

Mines completely missing.

[phatvtcom]

yea its just the little rubber hose thats come off, ive had the same problem on my LPG system aswell. I took it back twice to the gas converters and they ended up putting a tighter hose because it kept coming off constantly. I had some chugging on ignition too. Just take it to a gas converter joint they should do it for free on the spot, it takes like 10 mins

[whitey66]

The purge solenoid is at the back of the engine on the driver side.The plastic hose goes through the inlet manifold and is a bit hard to get to.
A lot of gas systems on these cause the engine to backfire,and this can blow the vacuum hoses off.But after saying that,even non gas cars can have this problem too.
You can put them back on with a pair of pointy nose pliers and some superglue,takes me about 2 minutes to do now (i've done heaps of them).