Don't waste any time or money on any manuals other than a Helms manual. They publish the factory manuals that have , by far, the best, most detailed info. Try something like
www.helmsinc.com or such.....
The code basically means that one side of the engine needs a dramatically different closed loop fuel correction (or "trim"). There is an O2 sensor on each bank and the PCM looks at the engine as two inline four cylinder engines for the fuel trim since it only "sees" those four cylinders on that side with any given O2 sensor. Since the engine should operate the same cylinder to cylinder and bank to bank the fuel trim should always be pretty much the same side to side. If not, then there is a clue that an injector is malfunctioning or something similar.
Based on the rough running and fuel trim imbalance it sounds like an injector may be sticking open...or not opening....
You could go thru the injectors at idle pulling one connector at a time to do a cylinder balance test by disabling one injector at a time to see if any injector sticks out as a problem.
If your post is correct and no typo and you have a 1999 then you have a Northstar and this post might be better off in the Northstar section instead of the 4.1/4.5/4.9 section as you do not have that engine.
Re: need source for 99 cadillac service manuals 
