So I took my D16A6 powered sandrail out to the dunes for the first time last weekend! It was freakin awesome! but I was having some issues with throttle response, it idles great and stays running by itself, when I crack the throttle it hesitates, then revs up like normal. While driving it, around 1000-2000rpms it surges making it hard to "put around", it wants to be ***** to the wall all the time, it comes alive when you put your foot into it! I thought it was a MAP problem, but I ruled that theory out. I couldn't find any vacuum leaks either. I'm kinda stumped. Heres what I'm working with, hope someone can help.

1991 D16A6 (stock)
Wired OBD1 running PO8 (stock)
My custom built header (no O2 sensor)
Walbro 255lph external fuel pump

I put about 80 miles on it in the dunes last weekend, it has plenty of power and was reliable, so I know this has to be a minor issue....

 

Oh yeah, I have the two vacuum sources on the front/top of the throttle body open, I tried plugging them and it didn't make any difference. I would have thought those would basicly be vacuum leaks. ????