Limp Mode if above or at 3500 Rpms for a couple seconds

2004 325i | 140k miles | Steptronic | M54



Current Codes:

P0174

System Too Lean (Bank2)



P0153

02 Sensor Circuit Slow Response (Bank 2 Sensor 1)



I've been having to drive the car under 3000rpms at all times because if I go above that for around 5 seconds or more the car goes into limp mode. *The dash beeps, all the dash lights come on and sort of feels like the park brake activates for a split second, then I pull off to the side with the car jittering/hiccuping, turn off the engine wait a sec and restart it and works fine.



Usually I only have to go above 3000 3500rpms on steep hills on the freeway (which I drive almost everyday) or accelerate quickly. I can keep from going above if I stay around 55-60mph on the hills.





I've ordered the O2 sensor and am waiting on it. And am even having trouble locating the vacuum leak, already smoke tested and couldn't find it, hoping it's the o2 sensor just giving off a bad code.

I recently replaced or done:



Fuel Filter



Fuel Pump



Changed ATF



Spark Plugs



Fan Clutch



Intake Filter



Intake Boot



Cleaned the MAF



Belts and Pulleys



I know it's not the same but I figured it's worth a mention,I found something similar to my problem on a UK e46 M3 site and they said something about the alternator overcharging/going out or it being the actual O2 sensor/vacuum leak wondering if that could be it? Or a wheel sensor?



Would really appreciate some help before a start just spending $$ on random things. Thanks!