Specifics: 1991 Civic 3D STD with the D15B1 4-speed.

Hey, all
Just installed a new head gasket and distributor, after having the engine overheat and stall a few times. Now it is running strong, but under load, the PCM throws CEL Code 1. The o2-sensor and cat were replaced a few miles before the head-gasket.

Please, let me know if you have dealt with something similar before. Thanks in advance!