OrionSPL

I have just reinstalled my motor and I'm breaking it in without the supercharger and stock injectors. It seems to idle ok sometimes and other times it misfires. When cruising around 2000-4000 RPMs it is a constant misfire. When it goes above 4000 it pulls hard and seems to run fine. Also, it did trigger an O2 sensor LO code and a MAF 100 codeafter about 10 minutes of driving. When it threw the code the car seemed to run fine. The opti has just been changed and the wires are all insultated with split loom from opti to the plugs. Any ideas would be apprciated.