I found the same thing with my Flex. Strange, it loves the E15 (88 RON) ... purrs like a kitten on that.A friend has an edge and he was telling me how it seemed to be bucking and hesitant at times especially when accelerating. I hooked up my live scan tool and we road around. It was knocking something fierce and having huge ignition corrections. I asked him what fuel he has been running he stated 87 per dealership. I encouraged him to atleast run 89 preferably 91+. He filled witha tank 91 it cleared up and has been running 89 since with no problems. This wasn't a case of a single bad fill of 87 or a bad station. He said it was happening for weeks and filling up wherever he was and needed to.