Get a new O2 sensor. O2 sensors usually have a useful life of about 100000 to 150000km depending on whether it's made from Zirconia or Titania. If you get a half cut one, it's most likely already dying. Thus just get a new one and bolt it in. Without an O2 sensor, the car can't finetune the AFR during cruising, forcing it to run rich, which can reduce your fuel economy by 20 to 30 percent, so you lose more in the long run.

300 ringgit is not much, i paid 700 for the stupid Bosch Nissan OEM one my car uses.

You generally can't clean the O2 sensor as the assembly is sealed (aka : You can't clean it even if you wanted to). If it's dead it's dead. Just replace it.

As for all these "treatments", i don't bother with them, if you want to reduce friction in your engine, that isn't the job of a petrol additive, but the motor oil. Change your oil and it's filter regularly and you're good to go, don't need any of these products. The most i'd use is detergent for the injectors, and even that it's better to manually send the injectors for cleaning.

Also improving your octane above the car's usable standard is worthless. It's a MYVI man. Unless it's a Subaru WRX/Skyline/Evo in disguise, it can't take advantage of the higher octane fuel. Hell even my turbocharged car is fine with RON95 unless i up the boost to 11 PSI or more.

Don't really need to tune it back, most ECUs are self learning and given a few drives will get everything right. Just replace O2 sensor and it's all good. Although you may experience shit FC for the time being.

Holy butts. Mahal.

If you're willing, you can look up the Bosch or NTK part numbers can get the same O2 sensor for 150 ringgit. lol Honda really cekik darah man.

Too bad they only have the OEM O2 sensors for the R32/R33 and not the 34, and that's why i had to buy it from Nissan.