i have a 1997 ford probe and have replaced a lot of parts. the car hesitates and sputters a hair under and a hair over 2 rpms. until 2 rpms and after 2 rpms it runs fine. what is the problem???

Optional Information:
1997 Ford probe four cylinder

Already Tried:
all basic maintanance i.e. plugs,wires,fuel pump,all filters, etc