Toyota Techs Throttle body Question

I have been complaining about the performance of my 03 Taco since my purchase in Feb. Today I am replacing both cats and installing a set of ceramic coated headers. I have the air duct pulled off and I can see the butterfly in the throttle body, so I wanted to look past it to see how much carbon was there. I rotated the linkage and the butterfly only opens half way. Is this normal? Perhaps a vacuum operated stop that prevents it from fully opening when not running. I double checked to see that the linkage is as far as it will go. I can manually open the butterfly the rest of the way with my finger. thanks