I have no idea if adding 91 would bring it down. I haven't ever run e85. the other thing that could cause a reading that high is an exhaust leak. when I put my speed daddy headers on I had a pretty good leak where the front manifold connects to the crossover. you can put your had near the junction and feel the air coming out if it is leaking. it could also leak at the rear junction, but mine only leaked from the front.