Ok, got a 1990 Maxima SE that passed emissions in '02 with a C0 reading of 6.8 or something like that. The limit in Colorado is 20.000. But just a few months ago when I tried again, I got a 23.xxx. So I failed by a little bit. Here's the thing, new injectors, new fuel filter, new air filter, new MAF, new distributor cap and rotor, new NGK plugs, no CEL, no misfiring and somehow it's still running a bit rich. I can't figure out why. Pretty sure it's not the o2 sensor, but would that be a culprit? And how could I find out before I spend $90 on a new one? Also could it be the PCV valve?