Ok carrotsnax idk if this will fix your problem but it is for sure Spiced MSP's problem.
Under the intake manifold is a vacuum line with a 1way bypass valve going from Bank 1 to bank 2. If it is broken all the air will go into bank 1 (To Lean) And no air will go into Bank 2 (To Rich)
These pics were taken with a iphone so there crap but should at least give you an idea
Ok here is the bypass valve (broken)
The Red Circle is where you can take a mirror and see the actual vac line, The neon green is where the actual bypass valve and vac line are but under the top of the manifold
And here is an attempt to get a pic of my new one. (Tight fit)