Sounds like OBD-II, so you're 1997-up, right? You didn't say.
"Too rich" sounds like a HEGO sensor fault- which makes more sense than a MAP sensor, since HEGO sensors are hot and might not like being immersed. I don't recall the code offhand, but I can check - hold on...
OK, OBD-II Code P0171 (DTC 51) is "Fuel System Lean, indicated by a 'Rich' AFR correction factor." Yep - sounds like a HEGO fault - they tend to wear out faster than the MAP sensor will, and they're subject to a good deal of heat (which both wears them out quicker, and would cause them to not like bathing...)
At least, that's my initial thinking...
5-90