AF Correction +25% Pumping Brakes

[BlueSubeDude]

My random misfire is driving me crazy...

Symptoms:
I have an inconsistent misfire on cylinder 1. This usually happens after I pull out of the driveway and drive a few blocks to a stop light. When I approach the light I notice that the engine idles roughly and then settles out after a while. At this point I get the CEL for Cylinder 1 misfire. It doesn't happen all the time.

Observations:
I notice that my car idles smoothly when the car is cold (open loop) and when the car is completely warmed up I don't have the problem. It usually happens about 3 minutes after I start driving out of the driveway. I used the AP to look at the AF Correction 1 and have noticed that when I'm on the brake the AF Correction goes above 10%. As a test, I pumped the brakes and found that the AF goes all the way up to +25% and the engine rpms change. At idle the AF Correction hovers +/-8%.

Car/Mods:
2006 WRX Stock with K&N Filter. The Airbox has broken tabs so I tied the box down with rope (been running like this for a couple of years). Cobb Stage 1 Map (does the same on stock map). I also have a small evap leak somewhere, but it's been fine for over a year (p0442). I recently changed plugs NGK iridiums, 0.03" gap. Compression hovered about 150 +/-2% on every cylinder.

What do you guys/gals think?

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[Cobb Tuning]

If it happens while pumping the brakes, which requires vacuum power, it would likely indicate an intake tract leak (probably post-TB). It's possible the brake booster supply hose itself is torn.

Cheers

Lance

[BlueSubeDude]

Originally Posted by Cobb Tuning

If it happens while pumping the brakes, which requires vacuum power, it would likely indicate an intake tract leak (probably post-TB). It's possible the brake booster supply hose itself is torn.

Cheers

Lance

I checked the brake booster vacuum hose, and everything seemed okay. When I pulled off the hose on the booster side I heard a "swoosh" of air which indicates that it was holding vacuum. I sucked on the hose (I know...very crude and unsanitary) and the hose held a vacuum. The check valve seemed to function properly too. Would I need a stronger vacuum to check the hose?

Do the diaphragms in the brake booster ever leak?

So with your response my misfire sort of makes sense. I'm guessing that my car is still in open loop when I get on the brake at the first stoplight and doesn't accommodate for the extra leaked air from using the brakes, which results in a misfire. Is my logic sound or am I missing something? If this is the case how come only cylinder 1 misfires? Based on my understanding cylinder 4 is connected to the brake booster line and would probably be the cylinder that misfire.

I appreciate the help.

Thanks

[danger1138]

Happy new yeArs.. I read this thread yesterday, so i went ahead and pumped the brakes while car was idling and the AF correction 1 went from hovering around ~4 all the way to +25.. So maybe an intake tract leak.. How can i test for where the leaks actually coming from? Seafoam?

[danger1138]

Bump..

[nmlittlebigman]

DIY Leak detector
http://forums.nasioc.com/forums/show....php?t=2205161

[Cobb Tuning]

Originally Posted by danger1138

Happy new yeArs.. I read this thread yesterday, so i went ahead and pumped the brakes while car was idling and the AF correction 1 went from hovering around ~4 all the way to +25.. So maybe an intake tract leak.. How can i test for where the leaks actually coming from? Seafoam?

You can do a pressure or smoke test of the intake tract. As nmlittlebigman stated, there are DIY methods for a pressure test. Most Subaru performance shops (and other repair shops) will also have the ability to do a pressure or smoke test.

Bill