stockevokiller

I have searched throughout these forums and have found nothing related to my problem.

I have a s13 with a s13 blacktop. When it is cold in closed loop it runs fine. But as soon as it warms up and gets to open loop it starts to bog and sputter kind of like misfireing. But this only happens sometimes and only while in vacuum. When I hit 0 psi or positive boost(full throttle) the car runs perfect and has all its power and pulls to redline no problem.

What would cause a car to sputter (misfire) but only during vacuum(part-throttle)?

Any help would be greatly appreciated.

Thanks

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1989 240sx, currently under construction.