idling problem

Last sunday I filled my gas tank and about 5 miles later the check engine light came on. I also noticed about this time that my car acted like it wanted to cut off or lose its charge when I idled in park or even stopped for a red light or stop sign. This morning I filled my gas tank again (I was down to a quarter of tank) and got premium gas (I got the cheap stuff before) but it still acts like it wants to cut off while I'm at a stop light. Any suggestions on what I can do??

Sounds like maybe your oxygen sensor is shot for keeping your your air-fuel mixture at the right level.

The Focus is engineered to run off regular gas, do NOT put in mid-grade or premium unless the label on your gas cover tells you otherwise as you will ruin the motor.

Take it to your local Ford dealer ASAP and have them look at it.

Check for vacuum leaks before going to the O2 sensor, spark plugs, injectors, or fuel filter/pump. My 2000 Focus had the exact same problem, and I found a gaping hole in the hose that goes from valve cover to intake manifold. More specifically, it was in the rubber elbow that connects it down at the intake manifold. That part is subject to deterioration, as I have seen numerous posts to that effect on here.

If you open the hood while the engine is running and you can hear hissing, you'll know your problem is a vacuum leak.