1996 Monte Carlo 3.1 P0171
An FYI and Thank You Post. Danthurs Thank You for the info you have posted on this site. Your check list on this code was very helpful.
The car had the P0171 and P0300 code. It would intermittently idle rough and have trouble starting when warmed up. Turned out to be the fuel pump was failing. I had a mechanic troubleshoot this for me. It would run fine for about 20 to 25 minutes, then the fuel pump would heat up, and the pressure would drop just enough to cause hard starts and rough running. Replacing the fuel pump has solved the issue and no codes.