bad gas mileage other than new plugs what else can be done to improve
simplest thing is to get low rolling resistance tires. however, your driving habits (ex, avoiding jackrabbit starts, accelerate gently, avoid excessive braking, when in traffic don’t tailgate so close close that your alternating slamming your brakes then mashing the accelerator, etc) make a larger impact on your gas mileage than anything else will.
Make sure the car is running well, the thermostat is bringing the car up to temperature quicky and every thing @pyrolord314 said.
The problem with these vague questions now is the things that are not revealed.
- What is the actual MPG and has it changed recently. 2. What kind of daily driving is done with this vehicle 3. Is this a recently acquired vehicle
Don’t drive it. Technically zero MPG, but doesn’t use any fuel either.
Is the check engine light lit? If so, get the codes read at a chain auto parts store (free) and post the results here.
What kind of mileage is the car getting and how are you figuring it?
First priority, make sure the coolant reaches normal operating temperature. It wouldn’t be unusual at all to have a faulty thermostat in a 19 year old car, especially if it has never been replaced before.