catalytic converter or o2 sensor? on 2003 Hyundai Sonata

I just had engine rebuilt, now pick up is sluggish. Mechanic says needs catalytic converter. Does that sound right? What are symptoms of bad converter?

Asked by for the 2003 Hyundai Sonata
1 answer
BAD CATS WILL CAUSE LACK OF PWR ISSUE ALMOST LIKE RUNNING OUT OF GAS ON EXCEL. YOUR CAN CK THE VAC. IN YOUR ENG TO DETERMINE THIS. A GOOD RUNNING CAR SHOULD HAVE APPROX 20 INCHES OF VAC,INSTALL A VAC GAUGE AND EXCEL TO ABOUT 1500 RPM VAC WILL DROP AT 1ST THEN RECOVER IF IT STAYS LOW POSS PLUGGED CATT. VERY COMMON