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Old 05-23-2007, 12:47 PM   #1
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Default AFR at idle.

What AFR are people seeing at idle? How much variation?

I have a friend running a link with new RC440's, basically running the FM defaults. His car idles fine but will occasionally go from 14.7 to 15.8 on the AEM WB gauge. It takes the car only a second or two and then it recovers.

I don't think this is a big deal, just the nature of running closed loop at idle.

Opinions? Experience?

Jay
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Old 05-23-2007, 12:52 PM   #2
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Without a WB to confirm the AFR values, I can say that the NB AFR guage I has bounces around under cruise or at idle. I would say it's the nature of closed loop.

Dave,
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Old 05-23-2007, 12:58 PM   #3
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You can run as lean as you want at idle... Just too lean will cause the car to stumble and vibrate more. I run mine anywhere from 14.7 to 16/17... typically around low 15s though to avoid excess vibration.
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Old 05-23-2007, 01:05 PM   #4
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Quote:
Originally Posted by jayc72 View Post
I have a friend running a link with new RC440's, basically running the FM defaults. His car idles fine but will occasionally go from 14.7 to 15.8 on the AEM WB gauge.
Sounds good. Mine continuously swings back and forth from about 14.5 to 15.9 on the AEM UEGO.
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Old 05-23-2007, 01:07 PM   #5
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mine is usually bounces around in between 14.8 and 15.6...

not right at start up though... this is an idle AFR after it is warmed up correct?
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Old 05-23-2007, 01:20 PM   #6
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Thanks guys, exactly what I thought. I will pass it on to him.

Jay
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Old 05-23-2007, 04:11 PM   #7
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my car is capable of idling as you described, however I've found idle to be smoother when richer. 13:1 is glass smooth. stoich has the ocassional miss and shake. This was with EMU & 550s, Link & 550s, and now MS & 440s.

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Old 05-23-2007, 06:01 PM   #8
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Unless you are tuning for emissions, you should tune idle for the lowest MAP reading possible. AFR really doesn't matter. My mustang with a decent cam in it idles at 45 kpa, the miata at 27 kpa.
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