Under the hood, in between the throttle and the master cylinder. Threre is a vacum line that plugs into this device with a throttle cable, well take that out, and test it. make sure it works, hold the vacum input and try to pull out the output shaft make sure it doesn't move or is hard to move. Basically make sure it blows and sucks air when moving the output shaft. put some light oil [3n1 would work fine] down in the vacum input, and through the open area near the output shaft. Test to make sure it doesn't stick, and all is well. as long as all these things check out, that is not going to be your problem.
PS: I hope this is accurate enough, i've never done this on a Bonneville, but on my dad'* suburban'* wastegate controller was a similar operation. If you need me to take a picture of where this thing is, [my description wasn't quite all that great] i'd be happy to.
'89 SSE - GX3 -190k, 155k on body - Back for another ride.