Toyota Repair: emmision test fail, air flow meter, rich mixture

Question
I have a 1992 Toyota motorhome V6 3.0 w/29K mi. It runs great and uses no oil, however, the emissions CO at idle are 8 times greater than the requirement. I suspect a recent trip to a Toyota dealer is the reason. They did a fuel service and tested al the systems because the rig was w/o power. They never fixed the problem but charged me 8 hrs labor and sent me on my way even though the rig ran worse than before.  After several repair shops the problem turned out to be a rusted gas tank and a plugged fuel filter. The rig runs great now but will not pass emissions. I suspect the Toyota dealer did some kind of adj to try to bring more fuel to the injectors not realizing the engine was starved for gas. Now that the rig is getting the fuel as it should the mixture is way too high. Is there an fuel adjustment on fuel injection V6 engines to allow the correct mixture or is there some other problem that may be going on? How can I get this rig to pass emissions?

Answer
The fuel injection is controlled by the computer and no adjustments are possible, if the CO is still too high then the reason for this should be diagnosed, is the check engine light on? Some causes for an excessive rich mixture could be a bad air flow meter, a restricted intake system, a stuck open injector or a problem with the computer itself.