Where to start with error code P0137 and P0171?

Question

Vehicle is a '96 Chevy C2500. These are the only two error codes I can pull. Idol is rough, but runs fine under normal operation.

Vehicle had been sitting for 5yrs. Fuel pump replaced to get running again.

Just looking for advice of where to start.

Answer 1

HI there,

First, P0171 is for a lean fuel mixture on bank 1.

P0137 is for a faulty rear O2 sensor on bank 1, sensor #2. I would start by replacing that sensor, then clear the codes. It may resolve the lean condition. If not, then check for intake manifold vacuum leaks on bank 1. If there are any then it might  cause the lean fuel mixture and the rear O2 sensor codes.