91 Sunbird- Failed Emissions

I recently purchased a 91 Sunbird (4 cyl) with 145K. Drove it 50+ miles home on the interstate (runs and drives great) and did a test run through emissions just to see what I might be looking at. It failed on hydrocarbons (limit 250/read 286) and CO (by same margin as hydrocarbons)-- not way off, but still a flunky.

Since getting it home it has had an oil and filter change and the air filter changed (both of which it was due) and some good gas put in it. I am considering one of those "guaranteed to pass" fuel additives before moving onto more expensive experiments.

Has anyone on here had any experiences with any of these products or emissions issues? With the car's age and mileage I am fearful it may be the catalytic convertor but...the readings were not that far off. Thoughts?
Thanks in advance...

Might try the O2 sensor, if it is acting flaky, can affect emissions... hydrocarbons are unburned fuel, meaning it is running slightly rich.... usually a weak or dirty oxygen (O2) sensor