Loss of power, codes, etc. HELP

[str8lucK_]

Hey guys, I have an 07 B7 A4 S-line with a 2.0t, this is my first Audi and I got it dirt cheap.
Problems it has. I really have no power. When I first get on it, it will be okay but then all of a sudden just drop and RPM's will go up while not accelerating anymore. It was worse before but I cleaned the catalytic converter. I can at least hear the turbo now. But also, I have a muffler/resonator delete and my exhaust sounds extremely muffled. It's nowhere near as loud as it should be. Below are the codes and the parts I've replaced. Thanks in advance.


Purge control valve
Fuel pressure regulator valve
Diverter Valve "E" model
Intake manifold flap motor
"R8" Ignition coils
Colder spark plugs
Fuel filter
AFE cold air intake
Gas cap
Muffler and resonator delete



P0171 - System too lean
P2004 - Intake manifold runner control bank 1: stuck open
P0455 - EVAP system: large leak detected
P0441 - EVAP Emmision control Sys: incorrect flow
P0234: Boost pressure regulation: limit exceeded (overboost condition)

[Jezza]

Is this a manual, because it sounds like you're overboosting due to a bad n75 valve. Overboosting like that could cause the clutch to slip and do exactly what you're describing. As for the codes, well, overboosting could cause those by breaking other components. I'm not a mechanic, just an enthusiast that reads a lot and does a lot of wrenching. I would research each of these codes individually first, if I were you.

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[str8lucK_]

It's an automatic, sorry forgot to mention that.
What is the n75 valve?
I replaced the n80 (purge control)

[Jezza]

The n75 controls the wastegate by opening and allowing pressure into the wastegate actuator. If it's sticking closed, the car will overboost. It's like a $50 part.

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