I am no expert but I think there are 3 ways to address O2 sensors:

1) Replace them and cross your fingers

2) Measure their voltage in operation (search for this info)

3) Get an OBDII monitor and monitor the O2 function that way. I have a ScanGuage II and I recommend it to anyone with a post 1996 car. It does just about everything you could imagine and comes in really handy at times like this. As I recall I had to program it to read the O2 sensors since that wasn't preprogrammed, but they explain how to do that. The guy next to me at work got one also and likes it, but we are both electronics guys so maybe that is why.

Keep in mind the O2 sensors may have nothing to do with your problem. The throttle actuator was mentioned previously. I don't know how those fail.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra