I have an EZ EFI 2.0 running E85. For the winter I switch the fuel screen to gas and dump in 5 gal. of Avgas LL100 for storage. Then when it warms up (In Nebraska, could be Feb, could be June unfortunately), I switch back to E85. On E85, I notice my AFR constantly bouncing from 8 to 14. The car seems to run fine. Could the little bit of lead in the LL100 have contaminated my O2 sensor?