Idle problems and cranking problems

There is a little confusion in the phrasing of your question. When people talk about idle speed it refers to the engine actually running under its own power. The computer in your car then looks at key sensor inputs and decides what idle speed the engine should run at controlling this speed using and idle air control motor or valve. What it sounds like you are experiencing is an uneven engine cranking speed which can be caused by a defective starter, defective battery or a voltage drop due to poor electrical connections at the battery, starter, starter circuit or engine block to chassis ground.