Reoccurring PO138 code

Hi.
I just purchased a 2010 Tacoma 4cyl 2wd

I drove it for less than an hour and the check engine light came on. I scanned the vehicle and it says it is 02 sensor circuit high voltage bank 1 sensor 2. I got an NTK sensor and had it installed. Drove it for 20 minutes and the code was back.
What else can it be or what is wrong. It does idle rough and has a noticeable spark knock. I had just filled it with premium gas when the cel came on the first time.

Can anyone explain what is going on? I can’t afford to pay for a garage to experiment with my truck.

 

How many miles on plugs and truck?

 

208550 klms on the truck. Not sure about the plugs. I have new plugs on order. Dansomplugs.

 

Start with new plugs.

 

Basically guessing without a scan tool but sometimes with Toyotas, the upstream B1S1 A/F sensor will trigger the code on the downstream B1S2 oxygen sensor.

If I were to suggest throwing parts at it, it would be B1S1. Otherwise it will need full diag.

 

^^ This ^^