SR Idles rough, then dies

[ProjNightshade]

Both my dad and I have searched the forums trying to find someone who ius having a problem like ours.

Here goes:
I have a 1995 240sx, and we swapped what we believe to be a kouki motor into it. Everything is hooked up correctly, and the motor starts.

However, when it starts, it starts idling high about 2000 rpm, then slowly drops down until eventually it dies on its own about 3-8 min later. In order to rev the motor, you have to very very slowly open the throttle plate, or else the engine dies. If you so much as brush the accelerator, the motor dies immediately.

We took it to a local shop to have them look at it, and they told me that the fuel pressure starts off in the mid 30 psi area, then drops off. This is with a walbro 255 hiflo, so I'm confused. I know it can't be the afm b/c the engine rev's past 2500. No one I have talked to has ever heard of a problem like this. It was explained to me that it is possibly the knock sensor, but I'm not sure. Has anyone ever encountered a problem like this one? I'm going crazy, and if I cant get it running I may have to part out. This problem makes me feel like this -->

Any help or guidance is more than appreciated. Help a guy not part out! Thanks.