96 nissan maxima

In a broad and general nutshell:

The Idle Air Control Valve does what it's name implies, it helps regulate the idle speed of the engine (at startup, when you turn on the A/C, etc.).

The knock sensor detects engine knock/ping and the car computer (ECU) uses this information to control the timing of the engine.

I would recommend having the IACV replaced, reset the ECU, and see if the knock sensor failure is re-detected by the car (you'll have to check the ECU for stored codes again in a week or two).

Cheers, Nirav