Every once in a while, when slowing down to a stop with the clutch in, the rev's will drop down to about 200 rpm's, then catch itself, and come back up to a normal idle. But today when coming to a stop, it dropped down all the way, and stalled. This is the first time doing this, but dropping down below idle happens about 2-3 times a week. I have been using HESS super unleaded, could that be it? Maybe a better selection of gas? any idea's?