Wanted S/H knock sensor

[1990timeismoney]

Hi all having problems trying to get eml of on the car error code is 52 knock sensor.I looking to buy a second hand one to see if the issue can be solved by using one that i no is not faulty before buying a brand new one.

Car seems to run fine A/f Ratio is ok but wont let the car boost properly.

Any help much appreciated

Luke