how necessary is it to fog an engine that has sat periodically for 2 years?

the gas in the tank is probably crap , the tank would have to come out to get cleaned and the fuel lines purged ,, moisture has gotten into the engine so you should remove all the plugs and shoot some tranny fluid , oil or whatever into the cylinders and turn it over without fuel pressure , you have your work cut out for you because sensors go bad and mice invade when cars sit , At times I have cars sit for months but I fire them up every 3-4 days and things can still go wrong