When I did the conversion on my 86, 12 years ago, the instructions I got with my conversion harness made no mention of the VSS sensor or hooking up PIN19. To this day it has no VSS sensor. And PIN 19 only tells the computer that the fuel pump is working. The only down side to not having it hooked up is the computer will throw a code saying the fuel pump has a bad ground.

So, what I am saying is, these 2 variables will not be your problem.

I would double check the wiring of the MAF to the computer(that they are in the right pins) and get a correct MAF for your application. See what happens from there.