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2006 Mazda6, 3.0l, automatic, 85000 miles. Wagon, silver with grey cloth interior.



While returning home yesterday, the car developed a noticeable stumble / misfire. The tach shows a short duration drop/recover when at idle, and the car hesitates and recovers when driven at suburban speeds. I've read a bunch of posts here, and coil-on-plug seems to be a common issue, especially at this mileage. Plugs were changed two years and 11,000 miles ago.



I've also noticed that the engine is putting off a lot of heat - Mom commented on this a week ago getting out of the car. Temperature gauge reads normal. Torque pro doesn't show any codes, and the CEL is off.



Any suggestions other than coil replacement? Especially with the excessive heat coming from the bottom on the car.



I'm fairly mechanical, but with T-Rex arms some things are just out of reach. Changed one rear shock myself last week, but had to get a shop to replace the other and front struts.
 

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With no CEL could be something other than a missfire. There have been Throttle Body issues with Mazda 6. Look through the forum to see if your TB model was one of the ones potentially affected. I would also check for vaccum leaks.

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2006 Mazda6, 3.0l, automatic, 85000 miles. Wagon, silver with grey cloth interior.



While returning home yesterday, the car developed a noticeable stumble / misfire. The tach shows a short duration drop/recover when at idle, and the car hesitates and recovers when driven at suburban speeds. I've read a bunch of posts here, and coil-on-plug seems to be a common issue, especially at this mileage. Plugs were changed two years and 11,000 miles ago.



I've also noticed that the engine is putting off a lot of heat - Mom commented on this a week ago getting out of the car. Temperature gauge reads normal. Torque pro doesn't show any codes, and the CEL is off.



Any suggestions other than coil replacement? Especially with the excessive heat coming from the bottom on the car.



I'm fairly mechanical, but with T-Rex arms some things are just out of reach. Changed one rear shock myself last week, but had to get a shop to replace the other and front struts.

I imagine that the mk.1 Mazda 6 engine runs similar temperatures to the surface of Venus. What that means is lubricants do not last like they would otherwise.


I would recommend new coils and plugs again (very soon!) The misfire is causing extra fuel to enter the manifolds and that is increasing the catalyst reaction which makes things REALLY hot. THIS IS HOW CATALYTIC CONVERTERS ARE MURDERED.
Mom ws right on. It probably is making more heat. Swap the ignition before the converters are melted. ↓↓↓↓↓↓↓↓






OEM replacements are:
DENSO 673 6005 - Ignition Coils x6
Mazda AJTT-18-110 - Spark Plugs x6 (these will be Motorcraft AGSF 22FSCM) {Plugs should be platinum or better.}



I would also change transmission fluid. I would avoid "flushing" but it is important to remove as much as reasonably possible. I did a drain and refill three times (11qts) with wonderful results.


All hail the wagon!


Good luck
 

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Status update if anyone stumbles across the thread.
It took a long time (family health issues), but finally got around to working on this stumble issue. Never set a code, so everything was a shot in the dark. Pulled plugs and found #2 and #5 oily, along with oil in the corresponding spark plug wells. Pulled the valve covers and started wholesale parts updates - PCV valve, throttle body gasket, EGR gasket, upper plenum gaskets, valve cover gaskets, spark plug well gaskets, plugs, coils, OCV gaskets, air filter and since it had failed before the air tube from the air filter box to throttle body. Cleaned MAF and throttle body. I had already drained / filled the AT with T-IV three times.

Once I got a vacuum leak diagnosed, the car has run very well. In retrospect I believe the spark plug gaskets and oil leaking was the vast majority of my issues.
 
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