backfire at 3krpm help(found the solution)

[scaramoche]

Ok, last week i finally got around to getting a new Catalytic, o2 sensor, and hooked up the AB valve. and now i run like sh##.
make a long story short, I ran fine before these 3 thinks were done.

I had the stock cat, o2 was bad, and had plugged the AB valve(where it enters the manifold). I rebuilt the motor around 9 months ago, and runs awesome...until know.

basically when i hit 2.8-3k it begins to backfire, loosing pressure, and i have no clue what's causing it.
things ive tried
reblocking ab valve
disconnecting o2
disconnecting smog box

nothing fixes the problem
help,...please, cause i dont know whats going on.

as a note, i thought/think it could abvalve, but my local nissan dealer doesnt have(took them 30min to find out what i was talking about), and they are not sure how long it would take to get.


UPDATE************************************************************************************
Ok, here was the problem. AB Valve.
and here is the solution.

To understand what i did, I want to explain what the AB valve does. In a nuttshell it regulates how much fresh air is allowed into the combution chambers.
From what i have researched/found out, the engine runs rich at higher rpm's, allowing more air in at these rpm's allows for a more "complete" burn, lowering unburned fuel(which causes backfire, when combined with air in the exhaust).

Because i cant seem to find a new AB, i started thinking how i could jimmy rig one. and here is my solution

Basically i removed my ab valve, but left the hose that connects to the intake. i then put my finger over the hose and had wife rev to 2.5krpm. It began backfiring like mad(wife thought i was going to blow something up) Either way, i slowely removed my finger from hose(allowing fresh air in) and backfiring stopped. the problem is if i leave my finder off it idles like hell, or stalls(to much air at idle).

so I came up with this solution

At the end of the hose i installed a rubber cap(used for terminating vaccuum lines and hoses, can be purchased at auto shops for 5 bucks or so) I then drilled a very small hole into the tip. This kept my idle good, and reduced, but did not completly rectified backfires. So slowely i made the hole larger, and finally found the sweet spot, Now no more backfires. So if your ab is bad, and you are having difficulty finding a new one, this is a quick and efficient fix.

NOTE: im still going to replace with a new ab when i can find one :P, but because this is my only car, i needed to find a fix