1993 Mercury Van Villager 93 Storage About 2 5 Years Start Engine Once While

i have a mercury villager 93, it was in storage for about 2.5 years, i start the engine once in a while, the car is still have half a tank of gas, now i start the car its engine kinda running not very smooth and check engine light is on. i have changed the air filter , sparkplug , try to put a bottle of octane booster with 2 gallons of 94 octane fuel to help the engine run better as the fuel was in the tank for 2.5 half year. The engine has some kind of hesitation when it running and not running very smooth.. any idea or help will be appreciated ..