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Old 08-16-2016, 09:54 AM   #1
dsirdah
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Default Bad MAP, MAF or O2 - Need Help

Hi,

My car is having a very weird behavior, my car is not having the normal power it used to have, and it seems to cut fuel supply momentary and then get back to life when I am slowing down. also when I hold the RPM at a curtain value Say 2000 RPM it keeps moving up and down by around 200 RPMs.

I have done some logging and found out that my STFT is very negative (-20%) and then it stays in the negative until I hit boost where it moves to positive (+7%) but then down to (-10%). my LTFT is always (-25%) and the best it gets is (-18%) and back to (-25%).

I am not sure what is wrong, but sometimes it get back to life again for short time and then it get back to the bad mode.

I don't have any faults.

i have uploaded the logs to the following link:
https://www.dropbox.com/sh/lj8w0owzy...oyG_Tpi3a?dl=0

i really need help to know what needs to be done to solve this issue.
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Old 08-16-2016, 10:21 AM   #2
STiSomeday
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Member#: 265430
Join Date: Nov 2010
Chapter/Region: MWSOC
Location: Cleveland
Vehicle:
2005 OBP WRX STi
IG - seriousblacksti

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Mileage and mods?
Air/Fuel and 02 sensors are wear items. I'd start with a new front a/f sensor, mine was slow responding without throwing a code for thousands of miles on my 05 sti.
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Old 08-16-2016, 10:32 AM   #3
dsirdah
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i am at 100K KM, i have Cobb SF BOX, tomei el header, invidia catted DP, IAG AOS.

my car is STI 2011 with a new short block Stage 2 from IAG. the short block is 30K KM old.
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Old 08-16-2016, 10:38 AM   #4
STiSomeday
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2005 OBP WRX STi
IG - seriousblacksti

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100k km with 30k being on a built block sounds about right for the useful life of the front air/fuel sensor. Sure, cars run much longer on OE sensors but the sensor response gets slower and accuracy decreases. A new Denso (OE manufacturer) direct fit replacement should be around $100 USD, maybe a little less. It wouldn't be a bad thing to replace as a maintenance item anyhow, and could be the source of your issues.
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Old 08-16-2016, 11:25 AM   #5
dsirdah
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Can you have a look at my log and see if it adds up.. Changing all sensors is a big buck, and yet it might not solve the problem.. I hate the guessing game.
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Old 08-16-2016, 11:44 AM   #6
bmxhotsauce
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02 IMPERZA WRX
BLACK

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i have a MAF sensor if you need one. works great no issues. shoot me over a reasonable offer.
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Old 08-16-2016, 03:11 PM   #7
dsirdah
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Thanks BMX.. I would like to know 1st which sensor/sensors i need to replace.

If someone can read the logs and tell me what to look for.
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Old 08-16-2016, 03:26 PM   #8
STiSomeday
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2005 OBP WRX STi
IG - seriousblacksti

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I can't confirm a sensor is bad just by looking at the logs. One bad sensor will throw everything off and that will be reflected in the log, but it won't tell me what sensor is bad because a bad MAF would affect fueling but so would a bad a/f sensor. A professional tuner may be able to pick up on certain things but I am not a tuner.

I would recommend replacing the front a/f sensor. It will not hurt anything to replace it, in fact the car will probably run better overall. Fuel trims are swinging all over as you mentioned, so there's a good chance the a/f sensor is part of the problem anyhow.
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Old 08-16-2016, 06:43 PM   #9
dsirdah
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Any tuners to help here??
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Old 08-16-2016, 07:38 PM   #10
424wrx
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14 legacy, 11 fozzy

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i had surging, weird idle fluctuations and it was my front o2 sensor. its done this 2 times in 8 years. both times for me the front 02 sensor was bad. just a thought.
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