[E4ODnut]

Old Mech,
If I understand your post correctly you are talking about engine braking, for instance, descending a hill, throttle closed. The theory is that if you open the throttle, engine braking would be reduced?

I agree with that. No theory, just observation. When I am descending a grade, throttle closed, I can shut off my fuel injectors. Minimum manifold pressure (max vacuum), no power developed in the engine. If I open the throttle the injectors will fire again, but, I can use manual control of my idle air valve to imitate a partial throttle opening. If I do this, manifold pressure increases (decrease in vacuum), still no power being produced, but the vehicle speeds up.