Originally Posted by trader4

That about covers it. I don't know why he's even fiddling with the DISA, it can't produce the sudden almost total loss of power he's experiencing anyway. It just fine tunes the mid-range performance and most people wouldn't even notice it if it's not working. If it's leaking air around it, that could account for the lean codes, but then it should be a gradual process, and not one where the car just suddenly loses most of it's power.

I'd focus on that P1515 code. Googling, not sure what it means, comes back with several different meanings. Checked Bently, they have no 1515.