Terminator 2

HI guys, this is my 3rd post, so as you can suspect, I am pretty new to all of this...well here's the deal...my car is getting around 5 mpg So, my problems are as follows....idle is suffering, there is a vaccum line off of the intake manifold or vortex chamber...whatever you call it. I have reconnected this, but then I get this TERRIBLE backfire! SOunds like a shotgun going off it is so loud. that's not a good thing. Anyways, the car feels to have nearly no power, and starting out from less than 3-4 grand will nearly kill the car, and I do know how to drive a 5spd...I was wondering if rotaries are just unique or need to be revved a little high in that regard. Next, my question is, if this isn't a HUGE deal (as I believe doing a rebuild is) then how much am I looking at spending? Also, I kinda hear a grinding like it sounds like my rear rotor is rubbing/wearing...this really worries me...seems to be coming from the back. I do not want to sell the car, but I also need to know how much I'm looking at. I love my TII (87) and my Talon nearly equally, though I am a little biased to my 4g63 Anyways, I appreciate your replies, and help this forum has done to help the Rotary community....thanks a lot guys