Codes p2096 and p2098 fuel system lean?

[4everRS]

POST CATALYST FUEL TRIM SYS TOO LEAN BANK2
POST CATALYST FUEL TRIM SYS TOO LEAN BANK1

My favorite light came on again a few days ago and above are the codes and description. Just ordered a vagcom so i cannot do data logging yet. After a little research, it looks like these are from the dowstream O2 sensors.

I have recently noticed a very faint whistle / hissing from the engine bay. The pitch of the whistle increases with RPM's. You really have to listen for it, but with the radio off and with low wind noise, it is there. Searching around shows that it could be various issues including a vacuum leak or even bad fuel. The whistle sound is very recent and I don't feel that this a coincidence with the codes.

Any thoughts? :confused:

[Shoppinit]

Unmetered air getting into the intake. Probably one of your hoses has popped off.

[Shoppinit]

Could be anywhere. Check the I/C hoses first, then the vacuum hoses. I've heard of mastervac hose collapsing and causing problems. Anything that is big enough to be causing your car to throw codes should be easy to find.

[4everRS]

Where would I find the mastervac hose?

[Shoppinit]

It's the one that goes to the brake master cylinder.

[Shoppinit]

You could get some leak detector spray from audi (p/n G0010800A1) and spray that around the engine bay. That should help you identify the origin of the leak.