Hunting / Surging when in closed loop

[deedadoo]

So I started the car up the other day and once it warmed up and went into closed loop mode it began surging and I saw the AFR jumping around a lot.  It will run lean for 5-6 seconds (~11 AFR) then jump up and down a couple times (~20 AFR) before returning and starting the cycle again.  

I didn't get any error codes which was surprising since there is something obviously wrong.  I unplugged the upstream O2 sensor and it now runs like normal, but I assume may run a little rich or not as efficient (although I haven't seen a noticeable drop in fuel economy or performance).  It's just now I have warning lights on the cluster and can't use cruise control.

Starting to troubleshoot now and am just looking for any advice if you've experienced something like this before. 

Thanks for any help.

 

Edited May 10 by deedadoo

[Scubaboo]

Thats a head scratcher.

02 unplugged and it runs better?  Have you tried checking livestream sensor data?

Maybe a vacuum leak?

[cww516]

I would have to dig through the service manual to verify this, but unplugging the front O2 sensor should knock it out of closed-loop fueling, since the front O2 sensor is the primary source of feedback for that feedback loop.  I'd second the vacuum leak theory, though, or maybe a flaky O2 sensor?  If you haven't cleaned your MAF sensor recently, that'd probably also be worth doing just in case, since it's quicker and easier than trying to spray every vacuum line in the car with brake cleaner or ether.

[deedadoo]

Thanks for the replies.  I tried looking at some live data through the torque app, but don't see anything jumping out at me - not sure if I know where to look specifically either.

I checked the O2 sensor and it seems ok (reading about 5 ohms).

Haven't checked the MAF sensor yet.

Will try looking for vacuum leaks.