First Check Engine Light

[Idaho Red Rocket 3]

After almost 3 years and 35,000 miles of driving and now we got the first Check Engine Light to come on with 83,000 mile total on the car. Buggers !

P1128. Bentley Manual has 2 lines printed with this code. The printed words for this code under "Fault Type" both say, "Oxygen sensing adaptation, idle range, cyl 1-3". Then under "Explanation" they say what appears to be opposite problem descriptions. One line reads "Short to ground / below lower limit / lean mixture threshold". The other line reads "Short to B+ / above upper limit / rich mixture threshold".

Nothing like having it read like it is saying something opposite. Can anyone please lead me in the right direction here ?

Thanks, Bill.