Ethanol does terrible things to the parts its comes in contact with. If leaves a gooey sticky residue behind, and is very "hot"...meaning it "cooks" things like rubber/plastic lines and gaskets., and there's plenty of parts like that in your fuel system. It is not meant for gasoline engines. Beyond and above everything else, corn is food, not fuel.
Anyways, octane is a fuel's resistance to spontaneous combustion. The higher the rating, the higher the combustion point. If an engine is set up for an aggressive spark lead and cranks high compression, putting lower octane fuel in it will cause the a/f mixture to explode before it is time, when the piston is in the wrong place. An engine set up for lazy spark lead and low compression is given hi-test fuel, and all of a sudden it is fouling plugs, running rich, sending raw gas into the cats, because the spark and compression aren't igniting all of the fuel before it leaves the chamber.
Run 87.