marco, take your car to an autozone, they will read the codes for free. if you have an indie close to you with a das system, then have him check the car. fuel filter needs to be changed every 60k miles, so if it hasn't been changed for that period, you should probably change it, fuel filter for your car costs like $15. also get fuel pressure reading at idle and after you shut off the car. could be the fuel pressure regulator
also try cleaning the maf with the crc maf cleanser and see if that helps. also could be the o2 sensor, or the throttle body. has the o2 sensor ever been changed? anyways, first thing to do would be to read the codes.