Ideally, there should be zero slack in the TV cable when the throttle is fully closed. (Wedge the choke plate open so fast idle speed isn't set). And at WOT, the cable should be pulled out as far as it will go.
On the very first one I ever adjusted, it appeared the cable was pulled all the way out at WOT. However, there was slack in the cable at closed throttle which made me drop the pan and do some detective work. Turns out the cable rod (on the trans end) was getting hung up in the cable housing, keeping the lever from moving the valve all the way in.
But anyway, it's not magic, nor does a pro have to do it.