Stuttering Issues....3sgte Options

[onlyfreddie]

I have a 3sgte in my Celica rev 2 JDM version from an MR2 Turbo. Could the AFM be causing my engine to buck hard when I go WOT? When I'm 1/2 throttle it runs as if I had it WOT all the way to redline its beautiful. I reset the ECU & it drives great then it will adjust after 10 mins then back to buck city.

-Cap/Rotor/Plugs replaced. Wires OTW
-New Walbro 255
-Tried race gas
-New Knk Snr
-O2 snr is completely black & I will be replacing asap (BTW is there only supposed to be 1 wire going to the o2?)
-AFR reads 13.20-13.80 on cold start then 14.50-15.00 after it warms up @ idle. 14.60-14.80 on cruise. 10.00 under WOT while bucking
-Vac sits at 20-22 at idle
-Boost is very responsive to throttle input. Spins 1st & 2nd on 1/2 throttle! It creeps to 10psi then peals off to 8psi towards redline. (3in EMS DP with 3in exhaust into 2.5 muffler)
-Only running 8PSI anymore makes it stutter really bad.

Any suggestions would be great....