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Old 11-01-2019, 12:23 PM   #1
Easyy
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2002 wrx
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Default Lean afr/bad idle, cant figure out why.

I just bought my wrx last Saturday and ive been having an issue that I cant seem to figure out.

At idle my afr gauge (passport) reads an afr of 17 and the idle sounds lopey. Car is running a OTS stage 2 tune from cobb and has a bigger tmic, catted downpipe, stock bov, stock intake.

When I unplug the MAF the idle goes back to 14.7. I bought a new denso MAF and that did not fix my issue.

I tried checking everywhere for vacuum leaks and I cant seem to find any. There is also a CEL for a misfire on all 4 cyls and fuel system lean.

Once the car is moving everything is normal, afrs read between 13 and 15 cruising.

Any ideas? I'm at a loss.
Car is a 2002 with 132k
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Old 11-01-2019, 03:07 PM   #2
snow_bound26
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Did you reset the computer after installing the new MAF? Do you mean Prosport? Not passport. Might need to recalibrate the O2 sensor for it or replace it if it's old.

As for the misfire. Have you checked your plugs and coils? Not that all 4 typically go at once. Crank position sensor can cause misfire codes. And lightened flywheels are notorious for it. Especially if they are combined with a light crank pulley.
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Old 11-01-2019, 03:18 PM   #3
Easyy
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Quote:
Originally Posted by snow_bound26 View Post
Did you reset the computer after installing the new MAF? Do you mean Prosport? Not passport. Might need to recalibrate the O2 sensor for it or replace it if it's old.

As for the misfire. Have you checked your plugs and coils? Not that all 4 typically go at once. Crank position sensor can cause misfire codes. And lightened flywheels are notorious for it. Especially if they are combined with a light crank pulley.
No, I didn't know resetting it was a thing lol. I usually drive an obd1 car so im used to dumb ecus lol. I will go try this now. And yeah, could be prosport, I'm just trying to recall it off the top of my head.

And the misfire, I'm pretty sure that its caused by the lean idle, its very lopey and rough at idle but instantly smooths out once driving.
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Old 11-01-2019, 03:35 PM   #4
NicMonte
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Quote:
Originally Posted by Easyy View Post
No, I didn't know resetting it was a thing lol. I usually drive an obd1 car so im used to dumb ecus lol. I will go try this now. And yeah, could be prosport, I'm just trying to recall it off the top of my head.



And the misfire, I'm pretty sure that its caused by the lean idle, its very lopey and rough at idle but instantly smooths out once driving.


After my Jdm swap on an 02wrx I had very similar issues.

I replaced front o2, maf. Fuel filter.(none worked)

Replaced injectors and fuel pressure regulator. This fixed the issue. I had the same symptoms. Also I would check your IACV this might be the issue for the looping idle(possibly).
Although, a boost leak could create similar symptoms.
Hope this helps
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Old 11-01-2019, 03:51 PM   #5
Easyy
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Just went and reset the ECU and went for a spirited drive. No dice, still idles lean. And yes it is a "prosport" afr, my bad lol.

Quote:
Originally Posted by NicMonte View Post
After my Jdm swap on an 02wrx I had very similar issues.

I replaced front o2, maf. Fuel filter.(none worked)

Replaced injectors and fuel pressure regulator. This fixed the issue. I had the same symptoms. Also I would check your IACV this might be the issue for the looping idle(possibly).
Although, a boost leak could create similar symptoms.
Hope this helps
I checked the IACV already, thing looks brand new. Ill look in to the fuel pressure regulator.
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Old 11-01-2019, 07:25 PM   #6
NicMonte
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Quote:
Originally Posted by Easyy View Post
Just went and reset the ECU and went for a spirited drive. No dice, still idles lean. And yes it is a "prosport" afr, my bad lol.



I checked the IACV already, thing looks brand new. Ill look in to the fuel pressure regulator.


Also what’s weird is when you unplugged your maf your car ran still...? When I did that my car turned off immediately. Which ruled out the maf in my case. But replaced anyways. My AFRs were loopy, jumping from low 13s to high 15s and occasional 17ish. When the FPR was replaced it fixed the idle AFRs. My injectors were a culprit of high af learning values and long cranks.

Look into why your car would still run with MAF unplugged. And go from there.(if I’m reading your post correctly)? I’m not familiar with Prosport? Is that a afr gauge?
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Old 11-01-2019, 07:55 PM   #7
Easyy
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2002 wrx
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Quote:
Originally Posted by NicMonte View Post
Also what’s weird is when you unplugged your maf your car ran still...? When I did that my car turned off immediately. Which ruled out the maf in my case. But replaced anyways. My AFRs were loopy, jumping from low 13s to high 15s and occasional 17ish. When the FPR was replaced it fixed the idle AFRs. My injectors were a culprit of high af learning values and long cranks.

Look into why your car would still run with MAF unplugged. And go from there.(if I’m reading your post correctly)? I’m not familiar with Prosport? Is that a afr gauge?
In most cars when you unplug your maf the ecu goes in to a default mode and corrects fueling by only data from the o2 sensors (at least from what I understand). This is why I thought my maf was bad, but I cleaned my old one and got a new one and it still idles at 17 afr.

And yeah, prosport is a brand of afr gauge. It reads constant 17 afr and the car sounds cammed/lopey at idle and shakes a lot. The second I start moving its fine and the afrs are what id suspect to be normal.

Car doesn't take long to crank, you turn the key and it starts right up.
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Old 11-07-2019, 10:11 AM   #8
subaru_gc8
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so what you want to do is unmarriy the cobb and see what your afrs are on the gauge, I had a prosport afr and that thing was a pos. I dont know what it is about their gauge but it always read differently, cant remeber if it was high or low but it was one or the other. So yeah honestly I dont think the car would run on a 17:1 afr to be honest.
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Old 11-07-2019, 02:10 PM   #9
Fozymandias
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Unplug your O2 sensor - if the issue goes away that’s your problem
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