I'd start off by making sure the right plugs are in there.
Double check the ECU to make sure it's a P07 (located in the passenger side footwell near the door under the carpet).
Is the EGR hooked up with the control box?
There is a normal stuttering that is inherent to the Z1 motor, coming into and leaving lean burn, but it shouldn't horribly noticeable.
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VX Info Thread