e90racer

My recently purchased tt is showing a check engine light and occasional EPC light. My understanding is that the EPC light is the "engine power control" and it puts the car into limp mode, is this true? I only drive below 3000 and haven't noticed any significant loss of power.

I bought the car with a Neuspeed intake, unknown exhaust system, and forge diversion valve already installed. I believe the codes were caused by the exhaust. Is this normal for aftermarket exhaust and be cleared?

The codes that came back were:
-P1116: Faulty HO2 sensor bank 1 sensor 4
-P1136: Idle system too lean
-P0134: same as P1116?

Also, my Forge diversion valve is making a fluttering sound. This is my first turbocharged car and I found out today that the flutter is a sign of air flowing the wrong way. Is there a way to adjust this or will it need to be replaced?

I'm not sure if the codes and DV have any correlation. Hopefully tomorrow I'll have enough time to take a look at everything and check for vacuum leaks. Any outside opinions and/or help is always appreciated!