It's saying, " Manufacturer Air/Fuel Mix " or the likes, on the CE computer at the local auto store.
I looked it up, and found this.
OBD Trouble Code: P1151 Lack of HO2S-21 Switch, Sensor Indicates Lean
My oil-dipstick has lost it's handle, so I pulled it out just a bit more to make sure it's not that.
The MAF sensor has recently been cleaned. (Alcohol Swab, barely touching it. I do known that the sensor did get slightly bent while cleaning, I don't have surgeon steady hands, haha.) I notice no difference in performance, other than the slow acceleration, poor trans. shift, and this new symptom, which I know is coming from one of the spark plug sockets.
This new symptom is the smell of decomp. Organic decomp. It's coming from the exhaust, but I know whenever I change spark plugs, I get one SP that smells of organic decomp. The last time I changed spark-plugs, I pushed a clean wire down into the SP socket, and black/brown 'decomp' came out. I have no idea how this s**t got in there, nor how to get it out.
But, the only reason I can think that this decomp symptom is related to the code is cylinder pressure.
Of course, that is if this website is correct.
All advice or help is appreciated!