[doru]

I would check the fuel pressure first. I "think" it should be around 75 psi, but I would first check the value first - maybe the New TIS has it, or someone can post it. If it's lower, say in the 30-40 psi range, then it could be a fuel pump issue. If your car is boosted, you have 2 fuel pumps - the HPFP and the low pressure one.
If all checks OK, check the cam sensors - when these start to go, you might experience same issue. As mentioned battery check see if it holds charge (turn vehicle off, turn on the headlights and leave them on for 5-10 min, then turn them off, wait a few minutes and check battery voltage).
If your car is not boosted, check the MAF as well.