I have a 1998 ES300 with 124,000 miles which is great in every way but one. When I take a trip and after running at expressway speeds (70-80) for about an hour, it starts to run rough when I let off the gas. As soon as I excelerate it smothes out again. Once it starts it will keep it up until I turn the car off for a short peroid, and then it runs ok for the next hour. Generally it starts when I top a hill and the cruse control reduces the gas when the car starts downhill. From them on it runs rough each time I let off the gas. Even at idle the RPM gage shows a 200 rpm oscillation and the exhaust smell like the engine is way too rich. I've taken to the dealer several times but they say bad gas or some equally vague answer. Any one have any suggestions.
Thanks
