Hi. I had the exact same problem on my previous 159. I went from workshop to workshop, and nobody had a clue what was going on. It just stopped accelerating as if the turbo wasn't working. (But according to the turbo/bar instrument the turbo was working)
So, I usually had to stop before any fault codes came on, but one time I managed to drive it a bit further. Engine light came on, and logging that there was a problem with the MAF. I cleaned it, and cleaned the EGR, MAP sensor and also cleaned the intake.
I thought it was sorted but after a little time: Same problem. Then I found out that I managed to pinpoint the problem when decelerating down a steep hill for more than 30 seconds. It happened every single time.
After a lot of research I actually found out that the turbo wasn't correctly fitted. There was a seal that was leaking from the intake side. This ment that the car had been driving too rich for 20k miles, and it had clogged up EGR, DPF and intake. So, after just putting in a new seal and replacing an intake hose all was good.
I don't know if this cam help you, but you should check it. My turbo was changed under warranty and the guys that did it didn't do their job properly...