Hissing noise after engine off

[Ryan_R]

I noticed a 103TSI (Mk7) making the same intermittent hissing noise when it was turned off the other week - so it must just be a software update that we've got.

[manny76]

Could be a vacuum leak. I had this on the missus' mk7 gti..... coupled with this the engine check light came on. It was the PCV valve......

Engine light came on due to ECU not being able to compensate for such a vacuum leak at idle.

Engine eventually began idling up to 2k then drop down to 1k.

Its possible that a technician has bumped a vacuum line off. Also check the engine oil dipstick. If the top "o" ring is worn it will also leak vacuum and cause a hissing noise.

Good luck.



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[tonymy01]

Manny, this thread is about engine not running= no vacuum. Only place with vacuum after engine stops is in the brake booster. You can confirm the booster check valve isn't leaking by pressing your foot on the brake before starting and listening for a low sound of air. Pump the pedal a couple of times and you will feel it becomes solid rather than softish(from the stored vacuum boost running out).

But yes,a vacuum leak in the manifold from pcv or other will definitely cause all sorts of probs as the MAF isn't measuring the true metered air going into the engine, mixtures will be very wrong and exhaust lambda won't match what engine is expecting= CEL.

[Ryan_R]

It's just the normal cool-down hissing sound that we're all used to - it's only changed so that it's intermittent now

[manny76]

Manny, this thread is about engine not running= no vacuum. Only place with vacuum after engine stops is in the brake booster. You can confirm the booster check valve isn't leaking by pressing your foot on the brake before starting and listening for a low sound of air. Pump the pedal a couple of times and you will feel it becomes solid rather than softish(from the stored vacuum boost running out).

But yes, a vacuum leak in the manifold from pcv or other will definitely cause all sorts of probs as the MAF isn't measuring the true metered air going into the engine, mixtures will be very wrong and exhaust lambda won't match what engine is expecting= CEL.

I disagree to a certain point. PCV was leaking down with the engine off. Try it, pull off the vacuum line with engine off. Yes vacuum leaks call all sorts of dramas very true. My check light came on because ecu can only compensate/work in a certain range to control idle speed. Once out of that range it logs a fault and light appears . I disconnected the battery to test and it would idle perfect for a day or so, then play up.

Initially I thought it just was a/c system hissing.

Sorry if this is a hijack guys, just was wondering putting a different angle on possibilities.

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[tonymy01]

? The throttle plate isn't a perfect seal closed, so if the engine isn't running, atmospheric pressure will be coming between air filter intake and engine valves. Vacuum is only in there due to the engine sucking air in while running. The crank case will have a little vacuum too from the engine vacuum via PCV, but that would dissipate almost immediately too I would think.

[90tsiwagon]

I have just picked up my 90tsi golf wagon. The salesman told me that when i turn the car off sometimes i will hear a hissing noise. He explained the car is pumping fluid to the turbo to cool it. He also said the hissing would last sometimes up to 60 seconds. Hope this helps
Cheers

[Ryan_R]

Yes we are all familiar with that - it's jut the nature of the hissing suddenly changed from constant to intermittent after the DSG recall which was a little strange

[shaguar]

I have just picked up my 90tsi golf wagon. The salesman told me that when i turn the car off sometimes i will hear a hissing noise. He explained the car is pumping fluid to the turbo to cool it. He also said the hissing would last sometimes up to 60 seconds. Hope this helps
Cheers

Agreed. That's what the technician told me as well but agree with Ryan that its strange it went to intermittent and not constant.

Also the technicians said its a self checking mechanism for the new transmission? (recall)

[xordis]

Add me to the list as well.
118TSI.
I had the recall fix done last Friday, and every time I drive it now it will hiss when I stop (maybe even when it's running?)
Seems consistent, 1 second on, 1 second off. I cannot see any fluids leaking underneath or in the engine bay.
I think it may have replaced the constant sound of the pump running to cool the turbo? Hard to tell as I was used to it.