95 XJ idle stumbles thn revs up and idles fine?

[Dirt Yota]

Like the title says. Jeep idles perfectly smooth, then will start to stumble a little then 'catch' itself and rev up to 1100-1200 and then idle perfect again. I've tried searching with no real positive answers.

This happens when the motor is completely warmed up(maybe when it's cold too but I havent noticed)

Also it's throwing a code 12 and 21. I assume 21 is the O2 and code 12 is the PCM lose of power deal(How do you get rid of code 12?)

Thanks alot!

 

[birchlakeXJ]

How many miles on that upstream oxygen sensor? Time for a new one most likely. I seek out NTK brand, which are the OEM supplier to Jeep.

The odds that you have a code (21) and symptoms are not likely a coincidence.

 

[Dirt Yota]

I believe it's original with 131k on it. I'm going to throw a new one in this weekend and see if it stops.

But what about this code 12? After 50 key starts will it just disappear?

 

[birchlakeXJ]

Yes, don't be concerned about the code 12. More informational than related to an actual issue.