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Discussion Starter #1
I've been told that a WRX should idle at 14.7:1 AFR. Mine does this when I first start up, and usually for a little while after. I've noticed that if I've been driving for a while (30+ minutes), and bring the engine back to an idle, I tend to read closer to 14:1. Any idea why this is?
 

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Your mods can change idle A/F. What are they?

<----(guesses atmopsheric BOV)
 

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A sensor that is wearing out requires more exhaust flow to make it read correctly. This could also be the reason why your at idle AFR's are strange.

As other have said, as long at the AFR's are correct when driving you have no issues.
 

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Discussion Starter #6
djrez4 said:
Your mods can change idle A/F. What are they?

<----(guesses atmopsheric BOV)
TXS TMIC
Helix Uppipe
Nvidia Downpipe
Bosal Catback
UTEC

Haven't bothered with a BOV yet.
 

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Discussion Starter #7
Hot_Dog said:
My A/F bounces around between 14.1:1 and 15:1 at idle. As long as its above 14 I wouldn't worry about it.
Occasionally I'll see it drop to 13.8:1, 13.9:1. But it mostly stays around the low 14s.
 

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Discussion Starter #8
stott said:
Could be a lot of things, but at idle doesn't really matter. The engine is under no load so there is not stress on any of the components. Worry about AFR under load.
What should it be at under load? Say... 20% TPS in 4th gear? I thought up to a point it should read 14.7:1 or 14.5:1, but I often see it read 13.4:1 under partial load.
(This is in stock mode on the UTEC)

I guess where I'm going with all this is to make sure my WB02 (txs tuna) is calibrated properly so that I'm producing exactly the numbers that the gauge tells me I am. I'm trying to get a baseline of what a stock car should produce at various loads/rpms to make sure my sensor is calibrated properly (yes, I ran the calibration for the sensor in free air)

I installed the sensor in February, but haven't really started to tune with it. Would the fact that it's been sitting in a catless exhaust for 5 months cause its readings to change?
 

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I don't have wideband hooked up at the moment. I am typically only paying attention at >50% throttle. Here was a run done on a Dyno with wideband http://www.stifiles.com/Dyno/ The images are fairly large.

You can see at idle I was running at 15:1. Running at 13:7 at partial throttle isn't out of the norm. Keep in mind the more throttle you give the more fuel you will be pumping into the engine and the richer the ECU is going to make the car. Stomp on the gas and watch how rich it gets.

If you really want to be sure how accurate it is, go get a baseline dyno run done and be sure they have wideband. Since you are running catless the exhaust probe will read pretty much the same numbers as your sensor.
 

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The ECU always shoots for stoich at idle and cruise speeds. When I watch my wideband when I first come to a stop, it's around high 13:1. Then it'll slowly correct itself after about 20seconds or so to 14.7-14.8:1. Same with cruise. It'll always correct itself to 14.7:1, or at least shoot for it as long as it doesn't max out the STFT and LTFT.
 

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Discussion Starter #11
Big Turkey said:
The ECU always shoots for stoich at idle and cruise speeds. When I watch my wideband when I first come to a stop, it's around high 13:1. Then it'll slowly correct itself after about 20seconds or so to 14.7-14.8:1. Same with cruise. It'll always correct itself to 14.7:1, or at least shoot for it as long as it doesn't max out the STFT and LTFT.
Thank you. :) I just needed to watch it longer. It indeed does return to the 14.7 range after 20-30 seconds.
 
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