2003 expedition "check engine soon" light
 

3 weeks ago my "check engine soon" light came on. I read in this forum that it might be the gas cap (2003 Expedition)..i changed it, and about 3 days later my "check engine soon" light went off. Then 2 days later it came back on?? I have noticed an idle difference at times, but not all the time?? Anyone have any other ideas. thanks deb