It surges because the computer is injecting a specific amount of fuel (it thinks) @ 39psi. It goes on the needs of the stock cam/engine combo. If you get more than about 20% out of wack, the computer is still injecting like it's stock, but that amount of fuel is no longer adaquate, so the engine begins to die. When that happens the computer tries to compensate, which it does, and overcompensates at that causing a rev, back and forth, so on and so on. The condition is only made worse by the conflicting information from emissions sensors and engine sensors to the computer.
The way to get rid of this problem is to set the fuel pressure higher than stock. When you do that, more fuel is actually being injected into the engine than what the computer thinks, and more air is going in than what the computer thinks so the ratios even out. Setting the idle up also helps this problem, but 1500rpms is a little higher than what I'd want to set it to.
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