Engine Runs Rough

Have a 2000 Mazda Miata with 40,000 miles, purchased new, under roof but not garaged, in coastal Florida. Last oil and filter change plus new pads on front brakes, machined rotors, 2 new drive belts, align front end. Now Miata runs extremely rough especially at stoplight idle. Dealer says I need new catalytic converter and that probably rust or something came loose inside converter and needs to be replaced. Does this make sense? Thanks for a mechanic’s help on this…I can’t seem to find anyone but Dealer to work on my 2000 Mazda Miata.

You or your mechanic can check your cat with a vacuum gague and knowing what to look for.
Do a visual inspection under hood for something out of place.

Is the Check Engine light on? If not, there’s nothing wrong with the catalytic converter. And if there were something wrong with the cat, it would be covered under the mandated EPA emission warranty of 8 years/80,000 miles for catalytic converters.


40k miles? Have you ever replaced the spark plugs. Sometimes a simple tune up can make a huge difference.