2000 Other Jaguar Models Poor mileage

Car is idling roughly and uses a lot of gas. I use premium. Have had spark plugs, air mass sensor. Eight rubber boots but not coils and fuel filter replaced and lots of expense. Vehicle is running a little smoother since the last(sensor) repair but gas overconsumption and sluggish is still there. Thanks so much for any feedback. I am retired and think I need to get rid of this car as I cannot afford the repairs.