[Boghog]

The knock sensor (KS) (Figure 2) detects engine knocking conditions and sends a signal to the power-train control module (PCM). A knocking vibration from the engine block is applied as a pressure to the piezoelectric element of the KS. This vibrational pressure is then converted into a voltage signal which is delivered to the PCM. The PCM then retards the ignition timing to compensate for the condition. The KS is attached to the engine block between the cylinder banks. The MIL will not be illuminated for a KS fault.​

 

[easterwabbitonearth]

sometimes the KS is at fault and causes timing that is too retarded and then slow idle speed

have had a couple where i had to unplug it, and made the idle much better

if the IAC valve is not dirty gummed, at fault.