Car is running good but gas mileage is not good as normal

Hello, diagnostic testing should be performed to see if you have an air/fuel mixture issue causing the fuel system to send more fuel than needed to run the engine. Unburned fuel can go into the exhaust system and cause major problems by overheating your catalytic converters also -- so it's important to check on this. Incidentally, problems which cause more fuel to be used than usual normally will set off your check engine light -- so if this hasn't come on, it might be that it's "normal" and driving habit related. You could also do yourself good to replace your engine air filter, as a plugged filter will cause some nominal fuel efficiency issues, as will worn spark plugs. www.repairpal.com/repair-shops