My car did not pass smog due to the HC being high

Could it be because or the Catalytic converter or bad mass airflow sensor?

Hi hows it going I have a 1992 Toyota Camry LE that did not pass smog due to having the HC being high. Mechanic said that it could be the Catalytic converter without even looking at the car. My friend connected his OBD1 and in the machine it came up that it is the IAC sensor Circuit and the ECT sensor circuit but nothing came up about being the Catalytic converter. And plus the check engine is not on. The only problems the car gives me it shakes when I come to stops.

But doesnt give me problems at all when I am driving it in the freeway only when I come to stops the RPM jumps a little bit. I dont feel like investing 500 dollars on the catalytic converter if at the end its not even that. I was just wondering if anyone might know if it could just be the Mass airflow sensor circuit. Thank you

Smog results HC 15 mph Max 81 Meas 100, 25 Mph Max 63 Meas 81. NO 15 Mph Max 554 Meas 744, 25 Mph Max 511 Meas 672