KNOCK SENSOR, WARNING LIGHT Options

[SandShark]

have a JDM st202 3s-fe 1997 ,, engine warning light has just come on

error code is 52 knock,21 oxygen , the car was fine and had
sat for 3 months without moving, then suddenly the engine
warning light came on after having just started it...

so did replace the oxygen sensor but still same code , 52 is the first
error code so presume that its the knock sensor, but that I am still
looking for something that may have cuased this error as the car sat
for a while ....any suggestions on other things that I could try..