I did my timing belt at 92k miles and noticed the low RPMs starting earlier the 90k miles. As soon as I did the timing belt, back to normal idle RPMs.
HERE is the post of my low RPMs and timing belt solution.
The problem with the ethanol is that when it sits for a while, it will separate. Most of the time in a car it is used fast enough and the movement of the car keeps it from separating. I know about this because I have seen it happen. I changed a fuel filter on a boat and used a gallon jug to catch the extra fuel, with in a week it had separated.