Well well well, after 2 years of this. I still have my beautiful Volvo but let say it is worst and more demanding than a girlfriend. I have over 200K miles on it. The same problem came back 8 months after the repair. The only thing I did throughout the last year is to erase the check engine whenever I felt some sort of misfire.

I believe JondevieonS40 is right, changing the airfilter (good one) will help since it has a connection with the MAF.

I just changed to fuel pump (used 150$) and I find my car engine better than before. I am not planning to waste more money now; My front window is cracked ($$$), the rain sensor doesn't work($$$), a drunk person hit my two tails light with a bottle of beer during the night (350$ used), left front side bearing makes a huge noise ($), the rack and pinion is leaking ($$$), my door lock doesn't work and got stuff rub during the night when my brother took my car ($$$$), my sunroof leaks whenever it rains ($$) blablabla.... I will never use Volvo again until they prove me their car is reliable. The worst thing is that I never raced or drove crazy with it.