I would check the output voltage of the maf both at the maf and the ecu (pin 42)(http://www.hyundaiperformance.com/forums/topic.php?t=44957). It should be around .80 or so at idle and rev to see how its acting. It may sound odd but check all your fuses inside/outside the car. Did you completely reset the ecu when you changed out the maf? Have you made any changes to the car recently before this problem occured?