I have the same issues (as do many I assume) Steve at throttlebodys.com will rebuild the 6G TBs. Pretty reasonable price. However, I don't know if it will fix your issues since I think it's more an issue of the FIAV that is problematic and there's no rebuilding that from what I can tell. That's the only reason I haven't spent the 150 bucks or whatever it was.

http://www.throttlebodys.com/DSMTBs.htm

cheers

poorman