PlatinumGLI

I was thinking of installing a BOV on my 1.8T but I heard that it might cause my car to run lean.

Audiboy

Probably, depending on how and where you drive. Bosch motronic leans out a bit for a brief period when the accelerator is depressed because instant dump of fuel on acceleration can wet the chamber. Adding a BOV may defeat that purpose I imagine.

Best to do is a hybrid one which a few people use but I don't know if they are adept at diagnosing cause and effect. If no CE light, then it means their way of driving and the engine condition can be compensated by the ECU.

One test would be is to take the car to the fast race track (not very technical). Drive a few laps, examine the spark plugs. Install the BOV, drive a few laps again and then examine the plugs. Darker means too rich.

Or you can log the O2 and fuel trim if you have a VAG.

Slightly rich is better than slightly lean but you are just overworking your cat and eventually foul out the spark plugs.

quattro5

turbines spinning slightly faster even, although i'd bet there's no perceivable difference in performance between the 2. worst is you're venting metered air per Audiboy's observation...

Žob

Cons=make car run like crap