Don't worry about what it reads at idle. Set the idle where the engine likes it and don't even look at the O2. It doesn't matter. The preferred idle mix on different engine combos is all over the place. Besides, there are several other factors that could affect the readings and confuse the issue.

Does your engine have much lope? If so, then the more lope at idle you have, the more that will confuse your O2 readings at idle.