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We recently bought a 2006 Mazda3 hatch (2.3L) with 186k miles. It idles a little rough but overall runs well but I am going through various maintenance tasks since I am not sure exactly what has been done in the past other than what is on the Carfax. Today is replacing the spark plugs. I went to my local Autozone and got a set of NGK LTR5IX-11 (4344) iridium plugs. I checked the NGK site and they said this one would work too.

BUT... when I pulled the first old plug out I noticed it is a LOT shorter. It is a Motorcraft AGSF32FM. Before I put in the longer plugs I figured I would check here first to see.
 

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I would normally call my local Mazda dealership but the service department was closed already. But O'Reillys, Autozone, Advance Auto, and the NGK website all think the new 4344 plug should work with my car so I went ahead and replaced them.

Tentatively I started her up, hoping to not hear pistons and plugs mating... HOLY CRAP, seriously? She idles soooooo... smoooooooth. Going for a quick spin around the block and pickup is better too. I had already changed the oil, air filter, cleaned the throttle body, and ran a couple tanks of gas with Seafoam through to help smooth the idle. Changing the plugs was just the next step, I wish I had done it sooner.

Looking forward to seeing what kind of gas mileage I get now. I was seeing 21 - 23 mpg mixed city and highway, but I have a lead foot so I was not overly surprised there.
 

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BTW, I am a little shocked that she was not throwing any codes. I have had the car for a couple months and 2,000 miles but just checked the ECU yesterday and it was clean as a whistle. Little troooper :D
 

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That's a little low for gas mileage, but it definitely does vary by the type of driver involved, so maybe no surprise to you. :) I am also using the NGK IX Iridium (4344) in my daughter's car and they work great!
 

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Over the past few months gas mileage has improved to an average of 25-26 MPG and I have a pretty heavy foot, so that seems about right. I get the same mileage in my Miata but I drive that like an idiot too :D
 
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