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Old 09-20-2016, 05:29 PM   #1
doinwork34
Scooby Newbie
 
Member#: 389051
Join Date: Apr 2014
Vehicle:
2002 wrx

Default strange stft drops and settles while cruising

I want to keep this simple at first.

While cruising at 8% throttle, my stft will gradually drop to -25% over the coarse of a second or two, and then stay there for another second or two, before I feel a lurch forward (fuel cut?) and then the stft comes back up to normal. According to my logs the AFR stays normal bouncing a bit around stoich through the whole ordeal.
Only happens like once or twice a week driving an hour or so per day.

I am trying to deal with a rough idle, slightly high fuel trims (3-8%) and some small knock events in the partial throttle range. DAM is at 13 currently...so im thinking this has something to do with it.

My only question is what the heck is going on with the stft?

I am think maybe a intermitten stuck or lagging injector?

I know I left alot of info out, but I am just wondering what could possibly cause the stft to do that.

Stage 1 OTS
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Old 09-20-2016, 11:09 PM   #2
06Limited
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Member#: 118112
Join Date: Jun 2006
Chapter/Region: MWSOC
Location: Chesterfield, MI
Default

Sounds to me like the car is dropping a cylinder at times. That would explain the poor idle as well. More often than not it winds up being either a bad coil pack. How many miles are in the car? What year is it?

If it a 2.5l car then you can log the "roughness monitor" for each cylinder. That'll give you a good idea if where to start looking.
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Old 09-21-2016, 10:45 AM   #3
doinwork34
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Member#: 389051
Join Date: Apr 2014
Vehicle:
2002 wrx

Default

its an 02 with 145k miles on it. I also need to check valve clearances. (I just had to rebuild my brothers heads since he burned valves so I am a little paranoid about mine) I had it stage 2 for a while, and only occasionally had spirited drives never really revving past like 5 grand. The car is surprisngly good shape; no rust or disintegrating hoses etc.

One issue that could lend to this is my leaky valve cover gaskets. But when I pull the spark plugs, the coils and plugs are perfectly dry...no oil anywhere on it. And the coils look to be in good shape.

How can I test if the coils are functioning properly?

I am planning on cleaning the IACV valve later today as well.

...Its just strange since if the afr is staying steady through the rich event, it would indicate that its not a sensor issue.
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