I have a 1991 Camry that's giving me fits trying to pass the emissions test. I failed first on high HC emissions, so I tuned it up. Failed the second test by 2ppm on HC. In both tests, all other emmissions were within limits.

Ok, went back and found that I had a cracked ignition coil, replaced that and went back for 3'rd test. Failed this time with high NOx emissions, but passed HC (FINALLY!) with flying colors.

I suspect either EGR or catalytic converter. I do notice slight surging at idle. I've read that if CO and CO2 emissions are OK, rule out converter.
Help, guys! I don't won't to spend a fortune on this thing. It's got 202,000 miles!