buckwild

hey,
recently my factory o2 sensors went bad so i put in a pair of bosch corvette rear o2 sensors before the swap the car run slightly rich ltft=-1to-4 at times, after the install of the new o2's the ltft varies from +5 to +12, and sometimes the banks will differ. the o2 volatage during idle and part throttle varies dramtically and drops down to .10 at times they also differ from each other at times they will go from .800 to .40 and so on changing im new to the tuning world and still trying to get an idea of what the o2's should read and at what time they should read it. at the moment im reading this with the real time data put out with the predator, im getting hp tuners sometime this week so i could log it completly with that and get idle part throttle and wot runs. well sry for such a long post im just looking to get some good info that i have only partly found with the search
thanks
-shawn

-not sure if it could make a difference but i did recently clean my k&n air filter and re oil it i didnt use much oil but wondering if any oil could get on maf and confuse it somehow
-also could it be an exhaust leak somewhere-