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Matt
Matt, Mechanical Engineer
Category: Audi
Satisfied Customers: 21870
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Audi

I have an Audi s6(5.2 v10), when the car is at correct operating

tempature there is a slight... Show More
tempature there is a slight whistle noise (seems to come from the gearbox), there are no problems with gear changes or any other issues with the gearbox, please note, the noise is still evident with the car stationary, any ideas?
Submitted: 2 years ago.
Category: Audi
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Shantal-Mod, Moderator
Satisfied Customers: 10
Experience: Moderator
replied 2 years ago.
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Matt, Mechanical Engineer
Satisfied Customers: 21870
Experience: BEng hons Mech engineering, in auto industry 22 years
replied 2 years ago.

Hello

This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.

As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.

Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.

if the engine condition is the same then chances are the meter or the connection to it is faulty

Air leaks are very temperature dependent as gaps can open or close up as things expand with heat, so the weather and engine temperature can effect them.

This leads them to be quite intermittent in the case of mild leaks

Customer reply replied 2 years ago.

with regard to the induction system, I have discovered that with the engine ticking over if you attempt to remove the oil filler cap there is a vacume in the rocker cover, with some effort the oil filler cap can be removed, once removed the engine cuts out.

is it possible the oil separator valve is blocked?

Matt, Mechanical Engineer replied 2 years ago.
Hello

its quite possible that the crankcase breather is stuck shut

so I'd suggest finding the hose that runs from the intake back to the cam cover and locate the valve and replace it
Matt, Mechanical Engineer replied 2 years ago.
hi

do you still need help with this?