I had a similar problem with mine when I installed an aftermarket fuel pump & wound the boost up, turns out the std injectors were bein pushed too hard with larger than normal fuel pressure & were in-effective at giving a proper spray pattern at low rpms but would come fine once the motor started to rev to.
Dont know if that helps or not
To fix it I got a Nistune-new injectors(660cc), changed fuel pump from Walbro to a Nismo pump, added a Sard FPR, changed plugs to copper & gapped the plugs to 0.7mm