I have personally seen wideband sensorS* fail in the manor you’re describing. Fine at cruise but below a certain reading (<12.5) they do weird things. I’ve seen both dead rich and dead lean output.
Is fuel pressure still tracking the 1:1 ratio? I know you’ve dealt with that issue in the past so I’m assuming it’s good.
Any logs with map/ afr target/ injector duty cycle/ fuel pressure? Timing could also affect afr...depending on who you ask.
