92 Cutlass Supreme Intermittent Problem

The Car: a 1992 Cutlass Supreme with the 3.1 v6
The problem: Sometimes, it it a little hard on the start, and randomly, while driving,
the idle will bounce up and down a bit. It's intermittent, annoyingly. Obviously specific conditions would help diagnose it,
but it seems to occur randomly. The check engine light will (sometimes) come on when this happens. Again, it seems to have no rhyme or reason to it.
It SEEMS like it's better in the morning on the first start, but again, only sometimes.
It seems to run fine otherwise.
To start, I think maybe the O2 sensor may be going? I've picked up a PCV just on general suspicion, as well as the filter set. Can't hurt to give em a change.
I was mainly wondering if any one here had any suggestions...
Am i on the right track with the O2 sensor? It'll be a bitch to change, and hate to do it if that isnt going to help, so I thought I'd toss it to the AF experts for evaluation. :)
Thanks

You are guessing at best here, many things can cause this, get the code/s read and post back.