Mercury cougar and disminishing gas mileage?

My '99 cougar use to get about 350-400 miles per tank it now get 150-200, the check engine comes on after filling gas but then turns off while driving, what could be the cause of this?
it has 79k on it, tune ups are around 100k not? also could the starter be the problem? and it seems to have lost some power.
 
Back
Top