Pref

I have taken the car to mechanic to check the camshafts and he said everything was fine there was an issue with temp sensor. I thought finally, it will pass.

But unfortunately it didn't help :/

However I noticed a new thing. When I plug my OBD2 reader and check post cat O2 sensor voltage, it remains almost static around 0.85v however if I rev it to redline couple of times and then keep 5k rpm for some seconds the value start fluctuating between 0.2v and 0.8v. the strangest thing is that when it start fluctuating and I shut the engine off and start it back up the value goes back to static 0.85v, but when it fluctuates and I keep the car running it just keep going up and down without becoming static.

Anyone know what this could mean?