stumbling after start

I've an 89 YJ manual 4.2, and the engine will stumble and accelerate roughly after a cold start. It feels like a severe loss of vacuum, but only lasts for a minute or two. What could this be? EGR valve?

Sounds like an o2 sensor to me.

are you losing coolant, oil, check all the plugs. More than likely it's not a 02 sensor. A 02 sensor only works in closed loop, that year vehicle, closed loop is at least 30 secs. check for a fuel leak down,

Well, not sure about the differences in years but my 97 was doing the exact same thing. 0s sensor fixed it. ( without engine code ) I know of several other people who have had the same problem fix. But again, not sure about the model years diff.

I replaced the O2 sensor back in June, but then I Nuttered it in July. Doesn't the bypass render the O2 sensor useless? It started this about three weeks ago, but maybe the Nutter caused it and I just didn't notice until the cold hit.

No major coolant or oil leaks, and the plugs were changed last week.

It's not a big deal and doesn't affect performance in any way after a few minutes of warming up. I'm just curious and hoping it isn't a prelude to some major mechanical breakdown on the horizon.

Anyway, thanks for the tips!