Rough start

2000 MAZDA MIATA
44,000 MILES • 1.8L • 4 CYL • 2WD • AUTOMATIC
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ALAN REINER
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  • 2 POSTS
Occasionally at startup it coughs (if this were a carburated engine I would say it backfires through the carburetor That's the sound I get. Then it settles in and is fine. I have replaced the following: plugs, wires, air filter, fuel filter, coil pack (Duralast). The check engine light indicates catalyst. I do not get a check engine light for intermittent misfire. Got that before I replaced the coil pack. Then no more. Any ideas? This car has only 44,000 miles and has been stored every winter. Never in rain or snow. I can't believe a failed catalyst would do this but there you go. Thanks Alan. Rochester MI
Jul 25, 2019 at 9:29 AM
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JACOBANDNICKOLAS
  • CERTIFIED EXPERT
  • 110,175 POSTS
Welcome to 2CarPros.

Is the code you get a P0420? If it is, you could have an issue with back pressure. Try this. Remove the pre catalytic converter o2 sensor and start the car cold to see if it changes.

Here are a couple links you may find helpful:

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Let me know what you and if that is the code you get.

Take care,
Joe
Jul 26, 2019 at 8:27 PM
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ALAN REINER
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So. I priced a new catalytic converter and found that for my Miata I could get an entire SS exhaust system with gaskets and hangers and nuts and bolts, free shipping for about $200.00 more. So without pulling the O2 sensor (there's only one and it's downstream of the converter) I pulled off the old system and hooked up the new one with Magna flow converter. Boom! Started without a cough. Cleared the check engine light, and life is perfect. You were right. Idles perfectly, and mileage is up. Power (according to my butt dyno) is better too, I think. It reaches red line fast. Thanks.
Sep 2, 2019 at 6:22 AM
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JACOBANDNICKOLAS
  • CERTIFIED EXPERT
  • 110,175 POSTS
Welcome back:

That's great news. It's amazing how back pressure causes problems. You are very welcome and please let us know if you have questions in the future.

Take care and enjoy.

Joe
Sep 2, 2019 at 5:39 PM