R32 gtst cutting out at 2500 rpm and blowing black smoke

[nes 1871]

R32 gtst cutting out at 2500 rpm and blowing black smoke

Hi guys and gals hope everyone is enjoying there holidays. Unfortunately iv got a couple of issues with bring my build back to stock. 

I upgraded the old rb20det with a bigger blower, injectors and mafless ecu al work was done at prestige tuner, car has never skipped a beat. 

The time has come to bring the old girl back to stock, enjoy it a little and move on to bigger and better things. i had to buy a s/h rb25 turbo (no shaft play and wastegate isn't seized), factory ecu and injectors, the airflow meter wire where cut short to the plug so i had to plug each wire into the AFM one at a time with blade terminals. Started the car and it is surging, cutting out and sometimes holding revs at 2000 rpm, blowing black smoke and the car will not rev past 2500 rpm without coughing and spattering (just when it hits boost). I come to the conclusion that the AFM could be the issue so i replaced it, cleaned my plugs which where black, and checked to see if my timing had been changed (it hadn't) and still no improvement at all ): Any help would be greatly appreacated