This is the same problem I'm having with MINE. If you find out let me know exactly what you did. I have replaced the servo with a new one...replaced the module...replaced the switch, checked the fuse, and the vacuum lines hold air just fine.
Andrew, if you're talking about the two vacuum lines connected to the servo, the big one is the break cutoff switch and the little one is the actual vacuum line that goes to the vac canister. You will only hear a hiss from the small one.
About the only thing I've seen that could be wrong here is the wires in the steering column...those are the only wires that really could be disconnected or something.
oOoOoOoOoOoOoOoOoOoOoO.... it worked temperamental!!!
i was out doing errands driving at 60mph.. then all of a sudden the gas kicks down and im going 70.. i never touched the switch... i hit the brake and it went off .. then i tested it again and it worked.. so i thought i was golden...