Re: Altering the AFR curve
This is a bit of a grey area here. On EFI engines the computer will almost always be trying to achieve an ideal fuel/air ratio. If you alter the engine mechanically (say a camshaft with bigger lobes to have more air going into the cylinders) but leave the same program inside the PCM, more than likely it will start throwing warning lights on because it will be unable to cope with the alterations within the parameters that are programmed inside it. Sometimes, when the mods are a bit too much, it will go into limp mode to protect your engine. Also, you need to consider that the leaner the engine runs, the hotter it gets and the more prone to backfire it is, so could end up damaging seals, plugs, leads, coils, heads, catalytic converters and so on. Your particular engine has a plastic inlet manifold that could deform & leak from overheating or crack if a backfire is serious enough.
On the other hand, if you change the programming to a more economy-oriented calibration, your PCM will know exactly when & how much leaner to run your car without causing dramas. The catch of course will be you'll feel that the car has less power. So, IMO, unless you're fitting a carby engine that you can manually adjust, a reprogramming is the easiest way to go. cheers