Ok so this is a very strange problem that I'm having a difficult time finding any information about. 2000 4.3, 5 speed. The engine runs fine when started up, no matter if its hot or cold outside. Idle speed is fine, no sputtering, no surging, nothing strange. Then I'll start driving and once the RPM's go over about 1500-1700, the engine will not idle down until I come to a complete stop.

Nothing I do with the pedals has any effect, doesn't matter if I'm in gear or in neutral. When coming off the highway or anything around 60 mph or higher, sometimes it will idle up to around 2200 for a second or two, then fall to around 1400 and immediately climb back up to 2000 where it stays until I come to a complete stop.

My issue is that I really have no idea where to start. I had the code read (my check engine light is on due to lack of a safety switch on my clutch pedal), and nothing new shows up. I can't just throw money at this thing, I'd like to at least have an intelligent starting point.

 

Offf the top of my head, I'd say you've got a pretty good vacuum leak , or extremely low compression.

Make sure theres no loose or broken vacuum lines under he hood especially the one connected to the intake.