I have a 2003 Olds Alero 2.2 150000 miles with high nox and high o2 and a very lean Lambda. Post cat ASM 15 mph co2 12.7, hc 1, co .14, nox 575 (allowed 443), lamda 1.13, 16.71 af. 25 mph co2 12.5, hc 1, co .17, nox 538 (allowed 730ppm) lambda 1.15, af 16.9 . ... Login to read more.