I actually live in Exton, but my office is in West Chester. Chadds Ford is a nice area.
I don't think this is as simple as bad gas. Over the last month, the car has been filled up with at the same two Mobil stations to which I took it during my tenure with the car. The only difference is that it is now being run on 87-89 octane instead of 91 or above. It is now consitently running smoothly at idle, while before, when running on a diet of 91 or above octane, it was consitently hesitating at idle.
I am essentially questioning WHY the accidental use of LOWER octane gas appears to have produced a good side-effect, so that I can duplicate this "side-effect" without putting lower octane gasoline in the car than the manufactuerer recommends.