My cat was replaced and my car is still chugging why? on 2003 Nissan Sentra

plugs replaced coils......please help

Asked by for the 2003 Nissan Sentra
2 answers 1 comment
BECAUSE THAT WAS NOT THE PROBLEM.HAVE CODES SCANNED AND POST
Check engine light on?
code was cat needed to be replaced....but got in car drove away from repair shop and still didn't sound right. More I drove back to the chugging sound like it was missing a cylinder as before......and yes light came back on not right away but within 2 days.....please help