It could be a few issues:
1. Feel the underside of both valve covers. If your hand comes back with oil, you have a leaking or seeping valve cover gasket, which is very common with WRXs and STis above 90K miles. That oil will burn off, and as it gets progressively worse, you can sometimes see some faint smoke coming out of the hood scoop.
If it does turn out to be a leaky valve gasket, do your best to find a knowledgeable friend to help you change them, many shops will charge way too much for this job that realistically takes no more than two-three hours.
2. Gas line seepage under pressure. Look into the gas line recall for Bugeyes. I live in Virginia and got mine changed out for free.