Something might have worn or come out of adjustment (like a wandering throttle stop screw) and this caused a low reading. If the signal return is below about .80 volts at idle, it should pop an adaptive limit code like you're seeing. I'd adjust my old one before buying new, but buying new is always an option.
Just checked it with the Tweecer .965 at idle and 4.707 at WOT. My KARMFs are WAY off though, like 1.2XX Could that cause large amounts of stalling at lights/no idle and bucking/not WOT power at WOT?
Yes and no, before I fixed the exhaust leak the check engine light would come on probably 3 times every time I drove to work. Now that I fixed the exhaust leak, it hasnt come on since....probably coincidence but its the truth!