HELLO! I HAVE A MAZDA PROTEGE 99 1.6 FOR ABOUT 6 MONTHS NOW! ABOUT 2 MONTHS AGO THE CEL CAME ON AND IT GIVE ME THIS CODE. ONE MECHANIC TOLD ME THAT I HAVE TO CHANGE THE O2 SENSOR . I CHANGE THE O2 SENSOR AND IN 3 DAYS IT CAME BACK ON. I WENT BACK AND HE SAID THAT THE CAT CONVERTOR NEEDS TO BE CHANGE? I WAS LOCKING TO BUY ONE BUT I FOUND ONE SITE THAT IT SAID THAT ARE 2 DIFERENT SIZES: 7.3IN AND 7.5IN? I DO NOT KNOW WHICH ONE!AND NOW THE CAR STARTED NO TO SHIFT THE GEARS. I GO ON THE HIGHWAY WITH 60MPH AND THE ENGINE REVS UP TO 4000RPM! CAN SOMEBODY HELP ME? WHAT CAN BE THE PROBLEM? I HAVE THE CAR NOW AT A SHOP AND THE GUY TOLD ME THAT THE CAT CONVERTOR IS CLEAN AND IS NOT CLOGGED SO THIS IS NOT THE PROBLEM! HE SAID THAT IS GOING TO INSTAL ONE CAT CONVERTER AFTER THE ON ON THE MANIFOLD SO I CAN GO TO EMISIONS TEST. I HAVE THE CAR CHECKED AT AAMCO AND THEY SAID THE PROBLEM IS NOT FROM THE TRANSMISION!!! I DO NOT KNOW WHAT TO DO!!!! PLEASE HELP ME!