I noticed a significant loss in performance and power in my 02 TT Quattro recently. The check engine light goes on and generates a system too lean bank 1 code.

After the mechanic hooked up the machine to the car to scan the codes, within 5 minutes (while I stood next to him), he concluded it was a faulty oxygen sensor. While I believe, it is a potential cause, its hard for me to believe he can know this simply by looking at the code, without further testing.

Today, I decided to take the engine cover off to see if I can find any clear causes of leaks and this is what I found (see attached, just to be clear, the picture is of the right hand side of the engine, with the engine cover off. further to the right, there is the MAF and air filter).

Prior to this, I cleaned the MAF with a cleaner (not sure if it helped, I felt like performance was back for a while, maybe, but it is gone now again, maybe the MAF needs replacing?).

My next steps is to either try to fix the below leak (if it a potential cause), replace the MAF or proceed with the mechanics recommendation of replacing the O2 sensor.

I appreciate any advice, if this is the cause of the leak.


Thanks in advance!