My lexus gs300 is sputtering like a real bad misfire when I step on the throttle like a quarter way down and I already changed the coils wires plugs and the fuel pump but after I put the new fuel pump it doesn't wanna start.

 

Are you getting fuel while cranking?

 

What brand fuel pump did u install? Do u have a part number for it? How did it run before you installed the new one?

 

I had similar issue, mine turned out to be air intake leak at resonator. Check air intake to eliminate that as a cause.