I've been dealing with a SES light for a while now. When i had it scanned i was told to replce the front O2's so i did with a pair of NGK sensors. The car was fine for about a month then the light came back on so i had it scaned again. I was told it's the front O2's again and that they are slow in switching between rich and lean. The shop sugested to try a different brand of O2's. I went to a different place to get a second opinnion and was told the same thing i was also told to only use Ford OE sensors. After i got home i decided to disconnect the batt. and change my plugs which needed to be done anyway. When i started up the car the SES light didn't come on and it stayed that way for about a week and now it's back on. So i'm confused if the O2's are tripping the light then why would it be off for a week after changing the plugs? There is a slight miss at idle that i can hear but that wouldn't give a code for the O2's would it? The miss was there even before i did the plugs but got no codes for it. So do i do the O2's or go after the miss?