One problem related to o2 sensor has been reported for the 1998 Toyota Camry. The most recently reported issues are listed below.
I have a check engine light that won't go away. Supposedly it was related to the O2 sensors. They've both been replaced, to no avail. A dual-certified Toyota master mechanic is scratching his head on this one. There's obviously nothing wrong with the engine as it's been performing well for the last couple of years, with an engine light burning brightly, regardless. It's very annoying as it's obviously a useless light, now, and all I can hope for is for the bulb to eventually burn out - as I don't care to get into tearing out the dash to remove it. Very very annoying (now have a piece of black duct tape over the lens but that's hardly a fix).