Engine quits at idle or when shiting from Parking

I had the car (a 2000 Toyota Camry; 4 cylinders)analyzed for problem indicated at subject and I am told (after two days in the shop) that they finally diagnosed to proble to be a bad charcoal canister (?) And because of that gas is bypassing it and getting to some valves. The cost of repair seems outrageous and I even think the problem may be as simple as water in the gas tank since the car was only started a couple of times in over a few months (the car is normaly driven by my wife and she suffered a fractured bone which has kept her from driving since Jan).