1998 Honda Civic D16y8 acting slow and check engine light o

Hello, I have ex with d16y8 engine with 250psi compression. I got the car with the check engine light bulb removed and after I installed a new one the light was on with this code: P0138 o2 circuit High Voltage (bank 1, sensor 2). Also recently the engine performance got weaker. Once I'm going up the hill the engine would hesitate and would increase speed very slow even when I have my gas pedal to the floor but after few seconds it would start to accelerate and pick up speed with the pedal still in the same position. It also happens on the straight road just when I try to accelerate faster. Also it kind of chokes when I'm in neutral (not moving) and I rapidly press the gas pedal and then rapidly increases rpm. I checked the catalytic converter by flashing light through it, looked clean and i could see the light through it. Also the timing is perfect, new fuel filter, distributor, sparkplugs and wires . Can you help me to find the problem? Thanks.