98 Chevy Tahoe choking

I have a 1998 Chevy Tahoe that when it is cold and first started will choke down and seem like its going to stall. Once it is warmed up (less then 2 min of driving) it will not choke down anymore but will hesatate when gunned. When the computer was checked it showed that it was a O2 Sensor error and was running rich. Any suggestions on how to fix this problem

You are probably going to have to take this to a mechanic. However, I would check the air filter first. When was it last replaced?