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Hi, I have a 2009 sti hatchback that I have had for a few months now. It was just protuned but iatuning a couple weeks back and ran great. Now it is running very rich around 10 afr when it idles, which it barely does. It used to idle at 14.5-7 a week ago. Planning on swapping plugs and cleaning the maf. I knew the previous owner and he swapped the upstream o2 sensor maybe a year ago. It has some bolt ones as well. Dw fuel pump and injectors, Perrin fuel pressure regulator, Cobb electronic boost control solenoid, aem cold air intake, tomei turbo inlet, catted turbo back exhaust.

Any suggestions on what could cause it to run so rich ?
ive looked over all the hoses and there doesn’t appear to be any vacuum leaks. Any help is much appreciated thank you
 

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Lets start with some more info first.

What kind of miles does the car have?
Is the check engine light on
Are there any fault codes stored?

It may be time to replace the MAF and oxygen sensors rather and than cleaning and swapping. Usually vacuum leaks cause lean conditions.
 

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What size injectors? That AEM CAI requires a tune (probably why you got a pro-tune). Like Jay said do you have CEL? I'd look at your fuel trims a and b should be +/- 5%. It's anyone's guess at this point but injector scaling and MAF scaling are what I'd be concerned with.

If you want to send me your map I can double check the injector scaling and compare the MAF curve to our AEM curve. I'm guessing it'll be locked though. Happy to work with you on an e-tune if you can't resolve this with your current tuner.

[email protected]
 

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Discussion Starter #4
Lets start with some more info first.

What kind of miles does the car have?
Is the check engine light on
Are there any fault codes stored?

It may be time to replace the MAF and oxygen sensors rather and than cleaning and swapping. Usually vacuum leaks cause lean conditions.
No check engine light at the moment but the sport mode and cruise light were blinking. The car has about 85k miles on it. And the upstream o2 sensor was replaced less than a year ago but that is a possibility. I’ll pick up a maf and see if that helps. Thank you
 

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No check engine light at the moment but the sport mode and cruise light were blinking. The car has about 85k miles on it. And the upstream o2 sensor was replaced less than a year ago but that is a possibility. I’ll pick up a maf and see if that helps. Thank you
I think you should also scan the car just to make sure there isnt anything stored in the system. It may also be a good idea to check your battery. Like Josh said above, you're going to have to start looking into fuel trim values along with MAF and Oxygen sensor voltages. This kind of issue is really going to require diagnosis rather than part swapping. If you want to try a MAF or primary oxygen sensor thats fine, i would highly recommend you go with OEM parts from Subaru and not the auto part store stuff. Components like MAF and oxygen sensors arent always made to the same spec as OEM. Just my 2cents.
 

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Discussion Starter #6
No check engine light at the moment but the sport mode and cruise light were blinking. The car has about 85k miles on it. And the upstream o2 sensor was replaced less than a year ago but that is a possibility. I’ll pick up a maf and see if that helps. Thank you

Update:

Changed plugs and cleaned maf. Night and day difference.idles way better and afr at idle is 14.6. The plugs were black. Which probably means it’s running super rich. I may retune soon. Thank you for the reply’s
 
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