The o2 sensors will tell the computer to make adjustments when you are at idle. This is much like if you have clogged fuel injectors, the system adjusts. I fuel with 1/3 e-85 and it should need less than 10% more fuel. This is within the amount of adjustment that the computer can make. It idles really smooth. Once I hit "clear self learn" on my Nissan Data Scan program and it idled really rough and had to re-learn. In the spring I will put it on a dyno and check to make sure the a/f ratios are good at high rpms but they should scale correctly. Then I will turn up the boost. I have about 3000 miles like this. This thread really describes what happens: