P12A1, Turbocharger Boost Pressure, Pressure Front of Throttle Valve too Low.
After putting in a new clutch and all supporting hardware I was reinstalling my downpipe and somehow stripped out the threads on the turbo manifold. I had a spare turbo I could use (F21 Frankenturbo), but after installing I got this code and the car wont stay running. The car ran fine before the turbo. Ive already replaced both fuel pumps and have decent fuel pressure. I have new coils and plugs as well.
If I unplug the MAF, it runs better but will die with throttle. I adjusted the wastegate some, as there was a good amount of play on the flapper...no successful changes. I took off the intake piping to ensure the turbine spun, its very smooth and spins freely. I cant figure this out.

Im probably going to end up replacing the turbo when I can afford to, but it sucks that I wont have the car for a few months until that is possible if I cant get some advice on what I should try next.

 

Enter the code here, and surf through the listings:
https://bmwfault.codes

Maybe something is disconnected still after the clutch job?

 

I checked everything plug-wise dozens of times, this is what led me to believe that the new turbo is at fault.
Thank you, I bookmarked the site for future reference. I plan on replacing the turbo for one without serious flapper movement. Fingers crossed that solves the issue.