when is it time for a new O2 sensor?

[Brendon Macaraeg <brendonm@xxxxxxxxxxxxxx>]

Folks:

Yesterday evening my car started very rough -- rough idling to
the point where I couldn't tell if the engine was about
to shut down or what.  After a few minutes of slow driving in my
neighborhood the rough idling went away.
It's a '96 328ia with about 84K on the odometer.
The car started fine today so I'm hoping it was just a hiccup.
But might it be time for a new O2 sensor?

TIA,
- -Brendon

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