240 sx, exhaust smells

[cocacola]

my 240sx exhaust smells. i know it is cat convert. mechanic changed out O2 sensor a while ago, seemed better. now smells is back, idles a little rough, when letting engine slow me down doesn't wind down smoothly. where is the computer hook up on this car (last mechanic couldn't find it and dealer is way expensive) help/// 1991 240sx

[drjohn]

Depends on the year. early models don't have diag. connector and use the ecm to get the codes.

[cocacola]

it is a 1991 240sx. sorry....