[HotZ28]

A bad 02 sensor, or vacuum leak, may be at fault here. If the O2 sensor circuit shorts out, or goes out of range, it may set a fault code. Since you do have a code, the sensor is basically, non-functional. In addition, if you monitor a good 02 sensor on a scanner, you could observe a rapid flip-flop between rich/lean.(5 to 7 times per second)
If it does not flip-flop back & forth quickly enough, this would indicate a

“lazy”

or, dead 02 sensor. If the sensor could maintain the air/fuel mixture around 14.7 to 1 (Ideal A/F), the output should read around 0.45 volts.