Because you get the same results with two different control valves, I would suggest that so much air is by-passing the throttle plate, even in the closed position, as to make the air flowing through the control valve irrelevant.
Could be that the throttle body is a bit worn where the plate-edge nearly touches the body. The stop-scew is intended to never require adjusting. Says who? As the vehicle wears on for many thousands of miles .... it will likely require adjustment. It is often best to replace the original screw with a bolt/screw with the proper threads. By removing the throttle body and holding up to sunlight ... we can make the stop-screw adjustment to the plate that ALMOST shuts of all by-pass air.