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ECU relearns the idle. Anytime battery is disconnected everything is set back to factory. Problem is, car is no longer factory new. Needs to relearn what's up, fuel pressure, vacuum, all the things based on current conditions.
Okay that makes sense, but how does idling for a long time help the ECU learn, as opposed to just idling at stop lights? And what effect does blasting the AC have on the ECU relearning?
 

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I don't know man, just do it. I'm sure it just speeds up the process and the AC on full probably just introduces another environment to the system.
 

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I don't know man, just do it. I'm sure it just speeds up the process and the AC on full probably just introduces another environment to the system.
Kk, I'll try. But can I still do this procedure and relearn the ECU even though it's been like 2 weeks since I last disconnected my battery?
 

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So I did it. Turned on car, shifted to D, stepped on brakes, idled for 22 mins, then blasted AC, idled for 15 mins, then drove.

During the idle time, never had the rough idle. As soon as I started driving, rough idle popped up again.

dafuq
 

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I know this is an old thread, but I'm working on this similar problem right now on my 2004 mazda 3.

I've done everything you've done. I also replace the PCV a month ago. Today I took out and cleaned the EGR valve. Still have the rough idle though.

I'm thinking of taking out the upstream O2 sensor (easiest to get at) and soak it in fuel for a few hours.

After that, I'm out of ideas.
 

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2012 Mazda 3 GX MT5
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Starving the engine will cause rough idle ... When engine is rev high it has the ability suck more .. more air and flow
(Simple remedies) Air flow & fuel flow...
  • Dirty Fuel filter and /or lines (this can throw a code if flow is very restrictive)
  • Dirty fuel injectors
  • Dirty air filter
  • MAF sensor ( this will throw a code )
  • Throttle body and the solenoids (
 
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