I'm just like you I bought the car from a mechanic that couldn't fix it for a customer and they couldn't come to an agreement on who was responsible. The car has alot of parts that where thrown at it. The mechanic was a duramax diesel guy and not a BMW guy. I'm like you I'm an amateur.

I've been working on mine for a few months as well. Plenty of boost off the line. I did a swirl flap delete and replaced all the gaskets on the intake manifold when I was in there.

The mechanic said he smoke tested everything, but I guess I'm going to get a smoke tester myself. I'm like you at a total loss and replaced all the normal things that seem to fix the problem but to no avail. Hopefully somebody will chime in. I bought a top of the line FOXWELL scanner but no ITSA.