What is wrong, is that your vehicle is exhibiting symptoms of LONG TERM NEGLECT due to the failure to do scheduled preventive maintainence.
From the symptoms you describe, it sounds like your vehicle is badly in need of a MAJOR TUNE UP by someone who KNOWS WHAT HE/SHE IS DOING, a qualified PROFESSIONAL TUNE UP MECHANIC.
Once a vehicle has deteroriated to this condition, the procedures [and number of parts] required to restore it are much to long and complicated to enumerate here. If you want to try the job yourself, you need to buy a complete "tune up MANUAL" for your specific make and model.
^^ Must be a mechanic needing customers. It's a bad O2 Sensor. Maybe along with a PCV Valve causing the shaking due to poor crankcase pressure.
I am getting a combined hwy/city average of 14mpg
Bad gas mileage can sometimes be attributed to a vehicle in need of a tune-up. Have your car serviced and see if that improves the gas mileage.
As long as it is running, & starting good, & getting good mileage, change them at 100,000 miles.
55 mile to gal
Personally, I get about 23 - 25 mpg. on my 1999 mercury mystique. I haven't counted high way mileage yet because I don't get on the highway alot.
I get 15.3 in my 2005.
18 MPG.
16-20 mpg is typical.
100,000 miles
If it is the 2.3L it probably has 8, 2 for each cylinder which is mainly for ease of starting and getting ~15% better gas mileage.
The 1997 Mercury Villager van has an EPA estimated city/highway mileage of 16 and 21 miles per gallon (mpg). The Villager wagon is also rated at 16/21 mpg.
no