Spit and sputter

My 280z has a auto trany.. When I take off the car runs fine when i get up to 25 - 30 mph then it spits and sputters if i hold the gas down the car will die I let up on the gas then it runs fine.

It starts fine and idles fine. Even if I'm just sitting and give it a little gas its starts to spit and sputter.

I put new plug wires and plugs in, new fuel pump and a new but used AFM.

Nothing is working.

The old owner did not drive it much and it only has 38000 miles. I had to change the fuel filter

as soon as I got it home.

The problem started after I sprayed the engine off.