Does it do it all the time, or just after the truck is warmed up?


Now that I think about it,only when warm.Hi idle until I stop.

Is it running hot at all?
No

I assume the CEL hasn't come on, allowing you to pull codes?
No

When the truck is cool, pop the radiator cap and check your coolant level. Usually if the coolant is low, though, it will bounce back and forth like that constantly after the truck is hot.... and won't stop when you rev it up.

I will look at that.

Beyond that, cracked/broken/disconnected vacuum lines will mess up your idle.

Thats why I replace them all. <img src="/forums/images/graemlins/smile.gif" alt="" />