Bought the car with 186k miles. Cel read knock sensor and o2 sensor. Replaced the knock and the rear o2 sensor. CEL went off for about a week then returned. Took it back to AutoZone and it read knock sensor and o2 sensor again. Will replace upstream o2 sensor this time but what's up with the knock sensor going bad again? Could something else be causing this?

Make sure the block surface where the knock sensor mounts is clean. Also do not over tighten the knock sensor. As for the o2 sensor they should have told you if it was up or downstream sensor. 

This time, they told me "bank 1 sensor 2"...which makes me think ita the downstream but the downstream is literally brand new. And ill have to clean the mating area and see if that helps. Thanks

Did they give you a number of the code like P0030?

CEL is still there. Haven't gone to get it read. Almost 100% sure it'll say both, knock sensor and o2 sensor. But the thing is, when I disconnect the knock sensor and the battery for about 15 minutes, and connect everything together, the CEL goes away and the car drives fine. But only for about 4 days. Then it returns and the car is extremely sluggish while accelerating and rough in between shifts. Doesn't this mean something is wrong? Lol I don't want to buy a new knock sensor if this one is still good. I've cleaned the block surface (somewhat dirty, can't get all of the corrosion off, but still pretty smooth) and the knock sensor (hardly dirty at all) at least 3 times now. If it's possibly in the wiring/harness, THEN what do I do? Any input appreciated.

Also, does anyone have any tips for a good safe cleaning agent to be used on the block?