Random misfire (2000 Chevrolet blazer 4.3 mpfi conversion, 4l60e)

Runs a little rough at idle, fuel smell, it has had a random misfire code on cylinder 4 twice(plug was fouled out once then replaced). Now it has a p1153 02 sensor code. I can clear the code again and it will run ok I’m sure but I want to figure out what the heck is actually wrong with it.