I have a 1995 isuzu rodeo 3.2L V6. When it cool outside it idles above 3000 RPMs at a stop. When you drive it down the road then push in the clutch the idle jumps back and fourth between 900 to 2000 RPMs. When you come to a complete stop the RPMs jump back up above 3000 RPMs. It keeps doing this even when the engine has warmed up.
First check for a vacuum leak from one of the hoses and/or intake manifold (gasket). Then check for dirty/sticking throttle. These are the easiest things to check so you do those first. Also, the reason the rpms fall when you engage the clutch: you're putting a load on the engine. It's design to do that.
But you're definitely idling too high. If no vacuum leak, scan computer.
December, 28, 2010 AT 9:38 PM
I agree, the above mentioned is most likely the problem, you may also want to clean/check/change the Idle air control valve(IAC)