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2002 Maxima Ghost P0300
I have a 2002 that I bought for cheap because the O2 sensors were bad. I drove it for a year the way that it was and it was getting around 28 MPG. Finally got some money saved up for new sensors, and changed them out along with the valve cover gaskets since they were seeping a bit.
I get in, start it up.... And now it runs like crap. Got the P0300 and have been chasing it for the last few months. I have put $700 worth of parts into it and still getting the P0300 code.
Started with the simple stuff. PCV valve, intake manifold gasket, and air filter. Sprayed ether around all the hoses and gaskets and it never stuttered. Moved on to a new throttle body, MAF sensor, and a new intake tube. Still rough.... (That tube was definitely bad, though, the only part so far that I know has really made a difference.)
Finally just recently did new plugs and coil packs and regrounded the MAF. It runs smoother now, but when I hook up my scanner, still getting a P0300. I look at the live data and the rear bank is for sure running richer than the front bank. The fuel trimming on bank is normally up around +7 or so while bank 2 is between -10 & -20. Every once in a while, the fuel trims front and back will even up, but not very often. It's been bad enough I burned out my rear cat. Got that replaced a couple days ago and all my problems are still present. Much less bad than they were at first, but still there. It does idle slightly worse in gear than it does in park/neutral, and also between 1500-2000 RPM.
I have heard the front engine mount could be a problem, what else am I missing?