It won't be trivial.Not to jack a thread, but I've been pondering the manual high idle myself. It occured to me though that if I don't intend to use my cruise control any more (truck is mostly an off road toy) would it be possible to hot wire the servo to hold the throttle?
Thinking that might give a little more control range. Thoughts?
My car uses vacuum for the cruise control, but whether it's vacuum or electric servo, it won't work to just "apply power". The cruise is a "control loop" - that is, the speedometer is monitored as as it deviates from the target either more or less fuel is added to get the speed back to the target. I have often pondered trying to rig a tachometer feed rather than a speedometer feed as the speed sense - but I've never looked deep enough to see it it would be practical. Likely it will involve multiplying or dividing the output of the tachometer so it looks like what the speedometer would send.
You could just try holding the fuel feed at a set position, but usually that doesn't work very well. It really needs a feedback control loop, especially once the engine speed gets much above a fast idle. Normally aspirated engines like the 6.2 will work better with the fixed position fuel feed than a turbo-changed engine will.