Idle speed is controlled by PCM. What problem are you having?
When you say knocking, do you mean an actual bootom end knock. If so that has nothing to do with idle speed.
My 2000 GMC Jimmy makes a knocking noise after it warms up. There doesn't seem to be anything else wrong with it, it runs fine otherwise. I have asked several mechanics and they are stumped. I was told it could be a wrist pin? It idles at 700 rpm, is that too low? What else could cause a bottom knock?
It is 12 years old. Not knowing how many miles are on the engine it could be an oiling problem.
The idle speed is usually onthe underhood sticker with the engine/emissions info.Most are between 650-750 at idle in drive.If it's just one or two wrist pins as suggested while it's running kill one cyl at a time and see which cyl. the noise goes away at.