Mileage decrease all of a sudden from 20 to 13mpg
 

Its about 6 weeks now and my van mileage is down to 13mpg no matter where I drive. I have about 37000 miles on my Quest 2005. I have never had any major service done on it. All I have done so far is just timely oil change.
Any ideas on this is greatly appreciated.

Check your plugs air filter and plug wires also check your fuel filter as well it might just need a tune up

How to test the fuel filter?
 

I checked the air filter and its pretty clean. I will have to open to front engine cover to get to the spark plugs.

hmmm
 

ouch... well if you do need new ones i would suggest platinum 2's