Lexus es 300

Sounds like a fuel issue. Has the fuel filter been changed? Did you resently purchase a tank of fuel, and it's possible that you get the bottom of the fuel tank from the gas station which is where all the water goes. You can get a fuel additive, plus fill it with fresh fuel from gas can. Eliminate the fuel as a problem because it's easy, and cheaper than having mechanic do it. Even if it starts running better, you found the problem. If you have water in the tank add some de-icer. They use that in colder climate states such as Minnesota where I grew up. During the summer months moisture builds up in fuel tanks, and winter comes and water settle's to the bottom of the tank, it freeze's, and the fuel pick-up is in the bottom of the tank and your stuck without fuel to carb...De-icer thaws out the ice, mixes with water, and burns up thru the motor. Good luck...just a hunch