1997 tiburon fx, 2.0 automatic..

was driving for about an hour and the car started chugging or stalling like i wasnt getting any gas or something, i couldnt get any acceleration whatsoever! it would eventually stall and die. but i learned that if im driving it for long and it does it, if the car is turned off and the restarted, it wont do it right away but eventually will, kind of like being reset. SO, took it to the shop, got the code"P1128". what would be the first logical thing to be replaced?? thanks -Nick