No other ideas, just similar experience... My car has done that on three or four occasions over the past few years, but it was only of short duration, at most a couple of days, sometimes for less than a day. About the only thing I can recall is that it seemed to occur with the onset of cooler weather, perhaps when I was only using the car for short hops and it didn't really get the chance to get up to normal operating temperature for a sustained period of time. For some non-rational reason I got the sense that it would correct itself, hence I didn't do anything to check the problem out, other than to take the car out on the highway for a while. Seemed to do the trick, but don't ask my why. Water vapor in the fuel system? Water vapor built up in the catalytic converter, thus screwing up the 02 sensor (I've had that happen too)?