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?
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.