I know this is horribly too little information. I got the car about 18 months ago from my father, found it had a leaky gas tank, which I replaced and then just let it sit. Now I've started driving it and after a couple hundred miles it spat out a P0455. Reset it and after putting on another 100 miles the monitor is still incomplete but I assume any mile now, it'll complete and kick the code out again. Other than a loose gap cap (interestingly this car doesn't have the spring flap over the filler neck) any other ideas or how to diagnose the problem (other than careful inspection of the tank and hoses).
