1999 Toyota Camry Engine problem

'99 Camry about 85,000 miles. Question guys, check engine light came on awhile back. Sometimes when driving and in acceleration, as much as i'm pushing the gas the car seems to want to go into idle and stay there, though i'm in drive and trying to accelerate. If I then put the gear into park, the rpm needle flutters up and down and the engine does the same. The code it picked up was bad 02 sensor running lean. As it's expensive to replace, I'm wondering does this match symptoms of an 02, or could it be something else? Thanks.