To test the butterflys on a dyno is a bit tricky since they are only active at lower power settings. It is hard to get repeated pulls at 20% throttle without a throttle stop. Proper block of wood under the pedal works. But then an automatic transmission hides all low power details due to the way the torque converter functions.

You can plug in and unplug these on a daily or weekly basis, keep a good log of fuel consumption and go with a SOP feel.

I kind of need to get back to testing but mine is a 3.8 so my findings will be a bit different.

Cheers, Charlie
If It ain't broke, Modify it!
87 Montero turbo Converted back in Spring1989
95 Montero SR 3.8 DOHC Only one?
93 Pajero 3 door 6G75 Mivec with paddle shifted 5 speed
Then a Gen2 SR with full coil independent suspension.