5-7k rpm o2 sensor reading????

OK so its been a couple weeks since I did the decat and muffler debaffle, my first o2 readings looked just fine. But I decided to recheck this weekend seeing how I was doing a throttle bodysync, and I've noticed the tone of the exhaust changes in different rpms (not the way it should). The exhaust sounds fluttery. What I've found is the o2 readings are 750-800 mv at all rpm ranges except from 5-7000. The reading drops right to 0 or real close to it, so that's no good running lean. The question is why? What is the ecm doing at that rpms that's different? The AIS is still hooked up but from what I've read the solenoid turns on at closed throttle and when under 140 degrees. So that should not be it. Any other ideas?

If that's just a static rev with no load I wouldn't dwell on it too much. I suspect it is running lean as there is such high vacuum for rpm and lack of work being done. Not saying its good, but I suspect its normal.

However I would inspect clamps at the base of the throttle bodies. They should be tight. You could also spray the area with starting fluid to check for vacuum leaks.

I was thinking almost the same thing on the way home tonight. In regards to the no load reading. I also thought its probably not a rpm its doing it but rather a certain position on the tps. I'm just seeing it at 5-7k because there's no load. With that said what's the ecm doing at say 5-10% open throttle?