Have you checked the little sock in the fuel tank that covers the line from the tank to the fuel pump? It's a pre-filter for the fuel pump and resides inside the gas tank. My ES was doing something similar after sitting for over a year except it would almost completely stop running. My sock was almost totally clogged.

Here is the proceedure. Get all of the gas out of the tank that you can. Have something handy to catch any remaining gas. Remove the access cover from the bottom of the tank. It is on the same side as the gas fill line. You will have to make the tool to unscrew it since it is square shaped. Just a little smaller that a 3/8 drive extension. When you unscrew it, all of the remaining gas in the tank will come pouring out! Be careful! If the sock doesn't fall out, use a set of needle nose pliers to grab it and pull. It's made out of nylon and is a press fit. I flushed my tank with fresh gas and re-installed the plug without the sock. It's been three months without the pre-filter and the car is still running great!