matt, I had the same problem with my 90'190e 2.6 a
long time ago. First, i replaced was the gas
cap.seems like odor was coming from the back.
air filter all clean(k&n) and then finally the canister purge. this is located in the left front fender, what it does is collect
vapors. simply take off the rubber cover on the fender and you'll see the canister and disconnect the hose and blow pressurized air
through for a few minutes. This will eventually get rid of the gas vapor(odor).