20:1 afr at idle but not all the time

some times when i drive my car it idles at 20:1 and very ruff but when i hit the gas its perfect (14-15:1) not sure if its lean because its ruff or the fact that its ruff makes it run lean. its not all the time. today coming to work it was fine just like yesterday but yesterday on the way home it idled lean. before it started doing this about 3 months ago it began to run/idle at 40:1 after if i shut it off when it was warm, ran in the bank or where ever, cam out and started it and it would be at 40:1 and i had to wait. after about 2 minutes it was if some one flipped a switch and it ran 14.7:1 perfectly. i keep thinking its a bad sensor. i plan to pull the codes after work today but what does this sound like to you? spark plugs are new, cap rotor and wires are a few months old, oil is good........

all the afr i gave are from my lm-1 wideband o2
 
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