Quin-Did you set the idle with the Idle Air Bypass motor disconnected? If not you should disconnect it when you set the idle, if after you plug it back in and nnothing chages and it still surges, the IAB is bad. You can try to clean it with some WD-40 just do not use Carb Cleaner or it will rot the rubber seal out.
Were fighting thios on my bud's 88 right now, although I think his BAP sensor is bad.
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FIRST TIME OUT 12.16@111 WHEELS-UP