Air hissing sound & "wobbly revs"

cianclarke

Just a quick question - today and yesterday I've been noticing a loud enough hissing sound coming from my 00' passat petrol. Seems to be coming from, well, the engine. After that I can't really locate anything, but basically the dead centre - when I pull the little lever for the throttle to rev, it gets a bit louder.

Also, after coming down from about 1500-2000 revs in neutral, it jutters up and down as if it almost stalled... Any ideas?

I'm pretty sure the t-belt is due a change, just gotten it booked in to be changed next week - but she's not due a service until another 4000 miles. Anybody?
Thanks

crosstownk

Sounds like a vacuum leak. Open the bonnet and try to locate the hiss - it could be a loose pipe or possibly a broken pipe.

The engine is stalling because it is getting excess (unmetered) air which is being drawn in through the vacuum leak.

layke

Loud hissing noise can mean your head gasket is gone.

To test, wait tilll your engine is cold pop the hood and remove the coolant cap.
Then you want to start your car in neutral.
Go round and tug on your throttle cable getting the revs up.

Now you want to be careful here if the problem is your gasket it will basically cause a buildup of pressure to your radiator so the coolant will shoot up like a geyser. You should also note a white foam forming.

If the hissing is very loud chances are it's not your gasket but better be safe then sorry.

Gerry

Check out the vacuum leak possibility first, its far more likely than a head gasket. In fact, it doesn't sound like a head gasket in the slightest.

With the engine running, check all hoses, starting from the air filter housing. If you see something that looks like a crack, either put your finger over it if possible, or spray some carb cleaner ( or failing that, a little wd40) at it, if the hiss stops or the engine note changes, theres your leak. It might be a crack in a pipe or just a clip that needs tightening. Best of luck.

cianclarke

Ah hah, problem solved! Thanks folks.
It was a pipe in the end, and a fairly obvious one at that - I don't know how I didn't spot it the first time I tried. On the offchance, does anybody know what the pipe is so I know what I'm searching for on eBay / elsewhere?
Photo:

Thanks!

crosstownk

I can't quite make it out from the photo - but where does that pipe go to (as it heads off into the shaded part of the photo)? I only ask just in case it goes to the brake servo - in which case you should replace it ASAP.

cianclarke

Problem is that I have no idea what any of the components are - it seems to just have air flowing through it.
It goes udner the throttle cable and feeds into something under the water pump - I'll take another look later and see. Thanks

crosstownk

The brake servo is a large circular component (10-12 inches in diameter). Usually it close to where you fill with brake fluid. Just follow the pipe and see where it goes. It may not be to the servo - but it's best to be sure, otherwise you run the risk of loosing servo assistance to the brakes making the brake pedal very hard and potentially dangerous.

cianclarke

Better pictures! Once again the one with the duct tape. It seems to be at one end from what I see going to a very long vent. Doesn't seem to go to anything circular - and I never noticed any problems with the brakes, it was just the revs.

http://sandeen.net/passat/engine_2.jpg This photo although not my engine gives a good scale of it too - it's going into what looks like a big huge seperator thing the orange tank with the blue cap and the dark tank with the yellow cap (can't recall off hand what they're for). Sorry about the terrible descriptions - if it were the inside of a computer I'd stand a much better chance!

crosstownk

Does it look anything like whats in the diagram in the attachment?

Turbulent Bill

Try to get your hands on a Haynes manual for your car, it should have good diagrams and descriptions of your engine.

cianclarke

Nothing whatsoevere like that - where it's going to seems to be pretty much the main engine block - it's all I could describe it as. More pictures again attached - but definetly not going to anything circular.
www.cianclarke.com/images/pipe4.jpg
www.cianclarke.com/images/pipe5.jpg

I also found 99 11 04 A stamped on it, but that doesn't seem to correspond to any VW part number.

In pipe4 it's the long rubber band that runs along the engine - which seems like a big narrow air vent or something.

In pipe5 you can see what it's going into - escentially the block with the huge pipe-like indents all to the top left.

Haynes manual? I've heard a lot about them, I must invest.. Thanks!

crosstownk

It's the opposite end to the engine block that concerns me. In the photo (pipe4) there is the brake fluid resevoir and the servo (the resevoir has the yellow cap). If the pipe terminates there then it relates to the brakes. TBH, it looks like it does - can you highlight the 'long rubber band'?

To eliminate any doubt, call to your nearest VW dealer and get a new vacuum hose. There is probably no immediate cause for concern, but it's always best not to take a chance where brakes are concerned.

cianclarke

Hi Crosstownk - the resevoir with the yellow cap is the other side of the engine.
That said I'll drop into a garage on the way back to Dublin and see if they have it in stock - I know there's one in Carlow. Thanks again!