Hey guys I've got a particular problem. I just bought a 95 F350 Fummins a few weeks ago. I've been working through some minor issues but this latest one is giving me some real trouble. Its got a motor from an 89' so its VE pumped. Anyway it will start to idle high randomly. It'll slowly creep up over the course of driving for a few minutes. The only way I get the idle to come down is to hold it in gear against the governor for a little while, Then it comes down slowly too. What could be causing this? I'm honestly lost. Was a 7.3 guy. Thanks

 

You're getting fuel (either diesel or motor oil) when you shouldn't. Must be on the hairy edge of runaway.
Full power screw set too hot.
Bad seal in the turbo
Piston problem.

 

I'd start with backing the full power screw out a 1/2 to 1 full turn and see what that does. Like j-martin said sounds like your on the edge of run away.

 

Next time it does that, poor some ice water on the pump. If it quickly drops to normal, your pump is shot.
You could also be sucking air into your fuel supply line.