As I'm driving on the hwy the focus starts to putter and lose power with my foot on the gas. This last time that it occurred I was driving 70 MPH and the speed of the car reduced to 45 or 50 as it was puttering (I did not floor it, I kept my foot on the gas as if I was driving 70 MPH). The engine light comes on when this starts to happen. I know that I can have a mechanic hook diagnostics up but I'm trying to avoid this. What is the likely cause of this problem?