I don't know if you've taken into a mechanic, but it's certainly worth a shot. They may know what's wrong and be able to help. Since you only have 70,000 miles on it, I would have a hard time selling it. It's such a young car by mustachian standards, that you're probably only now starting to experience the super low depreciation benefit of old cars.
Since your alternative is dropping $11.5K in cash for a new car, if a <$1K fix will keep it running for the next 5 years, that's definitely a good investment.