Are you sure the squeak is not the right rear seat latch "chirping" Mine does this, but I "fix" it every six months with a liberal amount of silicone grease on the latch mechanism and post. If it is not your seat, You may have luck with a small amount of silicone grease on your squeak.

Check you vaccuum hoses and the rubber elbows. I recently changed my abs module and then had a dramatic decrease in mileage. One of my rubber vaccuum lines was broken. After replacement of rubber line, mileage went back to previous levels. Volvospeed has a maintenance article on the rubber elbows.

Dash rattle. See:

http://www.brickboard.com/AWD/index.htm?id=637129

On milage. I have seen 19 mpg with 50% city/highway to
25.6 with 90% highway. So it varies greatly by how
you drive. My T5 has a computer that reads out the milage
and those numbers are across thousands of miles (currently
at 25.6 in past 2800 miles with about 90% freeway driving).

TRACS only engauges when one of the front wheels starts
to slip. It won't affect milage.

A stock air filter flows enough air for the turbo engine so
that is not an issue.

You might check tire pressure.

Is the 5 gallons what you read on the guage or have you refilled the tank? My guage is not at all accurate on my S70. Did the previous owner have the evaporator changed. If so the dash board bolts may not have been reinstalled or have broken.

TRACS will have little effect on fuel milage. You are getting 15 mpg. Is your tail pipe black? Are you doing a lot of idleing? Your computer will tell you your average speed, is it below 20 mph?

In other words, there are too many things to diagnose mpg problems.

Klaus
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95 854T, 88 780, 88 245