I wouldn't replace the MAF on a whim without having the car scanned for codes and working through all the other issues that can cause fuel trim/misfires. Granted, MAF's deteriorate over time and become less responsive to throttle and their base value can drift. Also, if you have already retrieved the codes from the ME (motor electronics) and have them written down, you can disconnect the MAF while the car is running crappy and if it improves you generally have a bad MAF (it will generate a code for MAF signal when its disconnected so you will have a check engine light if you didn't already have one, and will need to clear the codes after you reconnect).