I like how people tell him to get a real tuning software/hardware, instead of answering his question.
With my experiences on the AFC's, I have the Vafc2, you have to get the fuel just right for the car not to run like s**t. Are you using a Wideband or a Narrowband A/F gauge?
My car did the same thing, but that is because I forgot to turn my fuel down on my Vtec map. Try leaning it out around that RPM range since the AFC's work by controlling injector pulses and you could be so far into the positive side that its actually closing the injector faster? I don't know, I never had to put my fuel settings into the positive side it always stayed around -32 low throttle and -28 in high throttle which was still way too rich.