Isn't a lean condition when there is too little fuel getting into the engine? Maybe caused by a potential vacuum leak that reduces the air flow through the MAF sensor, and therefore, the computer does not feed enough fuel to the engine causing it to miss..? Maybe my understanding is a little bit simplistic..?
No AC. Running lean means that too much air is being entered into the combustion chamber for the correct amount of fuel. Whenever there is a broken vacuum hose or leak at the intake manifold, more air is being suck in than is required because the crack in the hose is also sucking in outside air along with the usual vacuum.. The O2 sensors sense this "too much air" reading and they tell the computer to keep the injectors open a little longer, adding more gas to compensate for the added air. Running lean could also mean that you have the correct amount of air entering, but you are not getting the correct amount of gas. But as we know, 170 and 173 are always set because of air readings.
Conversely, a rich condition is attributed to too much fuel entering for the correct amount of air. Therefore there is no way that the computer can add air to the overload of fuel, so it would have to command the injectors to stay open for a shorter duration than what is normal.
Although it is a little confusing, I hope I have covered everything..
Running Lean-too much air for the correct amount of fuel........80%...or
-too little fuel for the correct amount of air..........20%
Running Rich-too much fuel for the correct amount of air 50%
-too little air for the correct amount of fuel 50%