Once my car enters closed loop it picks up a low rpm miss and seems to lose power. It drives fine before it gets warm enough to enter closed loop so I am thinking it might be O2 sensor related. I have the Bosch ones in there and after reading some threads on here it sounds like they can cause problems sometimes. I just cleaned my MAF recently so I don't think it is that. Is there anything else I should check out?

 

I also noticed that when I was putting my headers on this weekend that the plugs seemed to be slightly white. Would this mean it is running lean?