The believe the only control you have for rich running is your AFM. Try loosening one of the 3" duct clamps between the AFM and TB and see if
the engine runs cleaner with the extra leakage air. If it does, then you're not getting enough air to the throttle body making for rich running. Might also want to clean your throttle body butter-fly flapper and the area inside around it. Do this with some cleaner on a rag, don't spray cleaner into the TB, it'll poison your O2 senser. Use a 0.010" dia wire to poke out the sludge in the tiny air weeper holes at the bottom of the butterfly.
10mpg! you may wanna check for some fuel leaks. When my car was getting crappy gas milage it turned out to be my fuel pressure regulator take the hose off and rev the engine and see if any fuel comes out of the regulator