usedcarjunkie

I bought a 1995 900S about 2 months ago, and have yet to pass inspection. The car only has 60K miles on it, and one mechanic did a fuel injector tratment that seemed to burn off alot of the built up carbon, but the NOx actually crept UP a bit afterward. The air filters been changed, vacuum hoses changed, wires, spark plugs, distro caps all checked, and no warning lights appear. The car runs fine. But I need to get the NOx down 50 more points to make it legal. The question is, will I be needing to sink a small fortune into a new cat converter just to pass inspection, or is there another way to adjust the engine to run a little less lean? I thought about changing the O2 sensor, but the mechanic said this wouldn't help the NOx. Any thoughts?
Thanks again.