Low gasoline mileage.

how long since spark plugs have been changed?

Hello, spark plugs can influence fuel economy indeed, but more likely present is a fuel trim issue which is causing dumping of fuel unnecessarily. This can be caused by lazy switching heated oxygen sensors for one thing. This can also be caused by an engine vacuum leak, or an excessive unmetered air intake leak. On the other hand, fuel economy is largely also related to environment, where you drive, how you drive, and the conditions where you drive. It might be that this is "normal" for current conditions.