I recently had a real problem trying to diagnose what I thought was a rich condition. I was using alot fuel and the shift indicator arrow was blinking. I checked the spark plugs (coated with carbon),temp sensor,fuel injectors,fuel pumps,pressure regulator,lamda sond and swapped out the main computer. What was really throwing me, was my understanding that when the car is in limp mode, it can barely get you home. In my case I was able to get on the freeway and pretty much go where ever as long as I was willing to waste the gas (and dirty my oil). Because I had purchased an after market AMM less than 6 months ago, and didn't believe I was in limp mode (which often indicates a bad AMM) I refused to blame the AMM. My mistake, and what a waste of time! I finally went down to the junk yard and bought an AMM for around $25.00. I have concluded that I was not wasting fuel because of a rich condition, it was running lean and was in limp mode even though I was able to reach higher rpms. I purchased the defective AMM on ebay months ago from OEM Parts. They replaced the part with no problem, the car has been running just fine now, but I will keep my junk yard AMM handy just in case. milt

Just in case you're not aware -- the most common cause of AMM failure is prolonged exposure to overheated air caused by a stuck airbox (the air filter housing) thermostat that continues to direct heated air (from the exhaust manifold, via the foil duct) to the AMM instead of the alternate, cool airway from the duct in front of the radiator.
I would inspect that thermostat, and even better (my personal preference*) do something to ensure that it never ducts hot air -- your AMM could last forever this way, IMHO.
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* I've personally used a dremel to literally cut out the whole flapper mechanism, and then seal the hot air opening with some "cap". From the outside, it appears (if you leave the foil duct in place) normal by any inspection short of opening the box (a real pain, and something state inspectors won't do).
Other folks have replaced the thermostat with a dowel that keeps the flapper closed against the hot air opening.
In any case, don't trust the thermostat.