I have a LO5 in my 1992 rs it passed emisions two years ago no problem with the same setup i did not pass this year because my unburned hydrocarbons are too high. I leaned it out alot and they got higher i dont understand this?
I put a new cat on it, new plugs, cleaned the iac, new o2 sensor and the hydrocarbons are still to high, although the CO2 is now under half of the alowable limit and the nox is fine what should i do?

 

it helps if we know what all the gases are, CO, HC, O2, CO2 & NOx.

high HC can be caused by the motor running rich, resulting in incomplete combustion.
high HC is also caused by running lean, that is called lean misfire.

check for vacuum leaks, all vacuum lines, power brake booster, TBI gasket, intake gaskets.
check fuel pressure.
a weak ignition coil or other bad ignition components can cause high HC.

you said CO2 is now under half of the allowable limit, do you mean CO?
CO2 is a by product of combustion, the higher CO2 is the better.

 

I meant co i was just in a hurry beacuase i had other things to do that day.

 

I know this wont help you any.. but I had the same problem with my 92 L03 in Texas...

I fixed my problem by moving to Louisiana