My Mariner used to get 22-23 mpg city/hwy.l am now getting a combined 15!l am driving the same, probably slower and with less acceleration (due to loss of mpg).l am getting 240 miles on 15 gallons... awful!
It seems like it started (or l noticed it starting) when l changed my air filter and oil/filter.It also seems to randomly be pulling left or right.
l have, in the last week and half, had a alignment, rotation/balance, and put the old air filter in.No help.
It is at the dealership right now.They are telling me nothing is wrong with it!Of course all they did was plug a computer in, not actually look at anything.
Has anyone experienced a similar problem with any vehicle?More specifically, a Mariner or Ford Escape?
Could it be a warped or bent rotor, disk, or caliper?

What you can try is using stuff by STP gas treatment. they have carb cleaners and fuel cleaners that help. l use it in my car all the time and it has helped a great deal.

Sounds like something maybe blocking the air intake. l have a 06 4X4 Mariner myself and never had any such problems. But the dealer servicing sounds familiar, lazy! Possibly something with a brake issue. Ask them to throw it up on a lift and inspect it.

try check for any gas leaks in the system and check your fuel tank.

It is got warranty, take it to another dealer who might care a little more.