Ye Ol' Cherokee

Hi guys.

So i bought my jeep 1 year ago, 98 cherokee 140k.

One of the main problems i have had since purchase is rough idle. Its not horrendous, but its pretty bad, sometimes worse than others.

Since i bought it, i have got a check engine light about 6 times, all of which it went off on its own. The first couple of times i got it, it was P0138, P0304, & P0305 which is downstream o2 sensor and misfire in cylinder 4&5. Now i never noticed the misfiring, but that could have been because it idles so poorly. Anyway, every time, it goes of on its own after a day or 2 and stay away for a couple months. Recently the past few times it has come on, it was just p0138. same story. Every time, no change in performance when its on or when it goes off.

It never stalls, and never feels like its going to stall. Always powerful and always starts right up. Just has rough idle. You can feel it fluctuating as your sitting in the seat, and you can see the RPM needle wiggling. This happens cold or hot.

The car had a tune up before i bought it by my buddy who is a jeep guy. He knows what hes doing and used champions and good wires

I have a hole in my muffler, not sure if this would have an effect on anything other than sound, since its after the cat.

Other than that, i'm not sure what it could be. Why would it go on, and then stay off for months only to return multiple times? and could a bad 02 sensor even cause rough idle?

Any thoughts would be greatly appreciated.

(Yes, i know, i can just check the plugs/redo the tune up, and just replace the o2 sensor, but i want to get as much info as possible before i start "going down the list"

In summary
-What can commonly cause rough idle in this jeep (And would p0138 have any effect on that

AND

-What could cause intermittent visits from my 3 old friends P0138, P0304, and P0305?

XRated

Clean the idle air control valve and replace the o ring gasket, you tube has videos and its a five minute job thats very worth a try.
I chased an at idle missfire for a while that would come and go but under throttle it ran fine. Changed both o2 sensors to no avail.
Cleaned IAC and cleared the code and its all good now.

I know its a older wrangler but the throttle body is the same so do what this guy did.