How do I repair codes 42 and 43?

What is your question?

After disconnecting and reconnecting the battery the vehicle will start and idle very well then start idling rough and shut down. After that it starts right away but shuts down almost immediately.

What makes this problem better or worse?

clearing the code by disconnecting the battery

How long has your 1991 GMC Syclone had this problem?

5-6 months. Didn't try to start it over the winter.