Volvo XC90 2.5T 2005

Have the PCV system checked to see if it is plugged up. If it is, have it cleaned along with the throttle body. Other then that, there really is not much you can do. Too be honest, I am surprised you even got 24+ on an XC90? Between 14-18MPG is about normal, especially a 5 cylinder. Also at fill up, do you reset your average speed and estimated miles per gallon? You should do that at every fill up. If your average speed is about 35-40MPH, your fuel economy will be poor. Over 50MPH estimated driving and your fuel economhy will show better since that indicates you are doing straight driving without slowing down like stop and go traffic.