I have a 1991 Century that I ran almost out of gas (it was literally chugging when I got to the station). Problem is, even though it has a full tank it's chugging like it's not getting enough gas. The check engine light hasn't come on yet, but I've gone from 30 mpg to about 18. I put in fuel injector cleaner, to no avail. What can I do short of taking it to the ol' garage?