Before you go and buy a new sensor, check the multi-plug that is located at the back of the engine on the intake side. Mine was corroded and not making proper contact due to engine washes. Had similar problems that got fixed by just cleaning the plug and spraying it with Q20 or WD40. Make sure that the knock sensor bold is torqued at the right Nm, otherwise it might influence it working operation as it picks up frequency.
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