Hey y'all,
So a couple days ago I got code P0139 (O2 sensor bank 1 sensor 2 late response). Thought this was pretty weird because I got that code less than a year ago and replaced the sensor, fixed the issue. The sensor I swapped in was third party so I just assumed it was a crap part. I had at this point noticed a slightly rough idle (intermittent), but the car still drove fine so I decided to sit on the problem for a couple days before getting a new sensor.
Well, yesterday that slight rough idle turned into a pretty bad rough idle and my engine started misfiring in all cylinders when I accelerate, and shaking really rough when I reversed. I figured the sensor crapped the bed and immediately went to Napa to buy a Denso replacement.
Put in the new sensor last night and it did not fix the problem. Engine still idles rough and misfires in all cylinders when accelerating, but oddly enough in reverse doesn't shake anymore (probably coincidental).

At this point I figured the ECU just needed to relearn a little, so I drove the car (city and highway) for about an hour to no avail. Still misfires cyl 1234 and rough idle.
Today I tried resetting the ECU using a method in a youtube tutorial where I remove fuse 6 and 9 in engine compartment box for 30 minutes then replace and idle for 30 minutes. Did not help.

I have not gotten any engine codes since replacing the sensor, besides the misfire codes. At this point I'm worried about engine damage, don't know where to go from here. Could it still be O2 sensor and ECU just takes forever to relearn? Wanted to ask online before taking to the mechanic.
Would appreciate any suggestions! Car is 2005 Civic LX 1.7L with 187k miles. Coils and plugs were replaced 5k miles ago and since it's all cyl misfire I'm ruling that out. Thanks

 

I've learned to buy sensors and anything else from the dealer , the price is worth the peace of mind , What do the plugs look like ? Try some injector cleaner .