stuttering 'stang
 

I have a '90 GT 5.0. The car barely idles. Below 2500 RPM it stutters bad, but above it smooths out and runs fine. I replaced the TFI module, coil, plugs, cap, rotor, fuel filter, fuel pressure regulator, air charge temperature sensor, TPS sensor, and idle air control valve. I am pretty sure the timing is set right. Does anyone have any idea what could be making it stutter?