BACKFIRE AT LOW IDLE, REPLACED UPSTREAM AND DOWN STREAM 02'S, HARD CODES ARE P1132, P1150, P1152, P0171. WE HAD REPLACED ORIGINAL MOTOR WITH 2000 FORD EXPLORER USED ENGINE WITH 26,855 MILES. DEALER HAS REPLACED ALL 4 CATS UNDER WARRANTY. ACTS LIKE IT'S STARTIN... Login to read more.