If you like where the lever arm sits at rest (and the butterfly valves that sit internal at that same position), do you think extending out the "post" that makes contact with the idle switch might be all you need?
Or is it that when you press on the lever arm all together, it moves a little more than what the springs will do by themselves? If the whole thing will move a little bit more with some force, then it's probably the springs on that rotating stem that the lever arm and butterfly valves pivot on that got weak.
I had my spring on the lower engine cover get weak from what was likely the heat or rust or age or whatever and the fix was to replace it. There may be a time where the springs in some of the spots on our cars are going to have given up their force to do their job and it might be soon in some cases.
I think the problem spring would be included on this assembly, but I don't know how you go about getting just a replacement spring.
http://store.delorean.com/p-6395-butterfly-assy.aspx