So the Idle Air Control Valve is what controls allowing more air into the engine to raise idle when there is additional need to increase rpm, thus spinning the alternator more to provide more amperage when high power needs are required. This also includes when you turn on the AC or turn the wheel and higher pressure on the power steering is required.
If the IACV is faulty it can cause a number of idle issues, from low idle, high idle or erratic idle (jump up and down). A lot of times cleaning out he IACV resolves these issues. If you manually power the IACV while installed you can also verify its function.
