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Old 11-19-2007, 01:01 PM   #1
bboy
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Member#: 56468
Join Date: Mar 2004
Chapter/Region: NWIC
Location: Seattle, WA
Vehicle:
04 Improved STI
Dirty White

Default Car is stalling under decel and coming to stop, help.

OK this is not my car, and I'm not convinced that it is a tuning issue yet.

The car is an 04 STI with modified stock injectors (scaled to 750 in Enginuity) with a Perrin BigMAF and a Turbosmart BOV (atmospheric). Rest of the stuff is typical.

Please don't lecture me on the BOV. I know its bad with MAF.

The car dies when coming to a stop with the clutch in. It stalls more readily if the brake is more forcefully depressed (less vacuum).

Logs of the period just before the stall show that the ECU is either pulling fuel or adding fuel depending on how I scale the MAF at low load.

Here is a typical scenario. The car is decellerating in gear, clutch in, brake lightly, RPM drops very low to 500 (idle is set to 950), car gently stops, idle drops to 200 RPM, car sounds like rich, but AFR can indicate lean, car idles in the 400-600 range for ~10 seconds, car recovers to normal idle at 950 and AFR of 14.7.

I cannot stress enough the long period of low speed idle before going to the set point. 10 seconds is a long time.

I've tried rescaling the MAF. I've tried unsuccessfully to eliminate closed loop fueling from the idle area. I can post a log but I think the description is more informative.

Driving me crazy, making me feel stupid. Please help.
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Old 11-20-2007, 11:49 AM   #2
06rexwagon
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Join Date: May 2006
Chapter/Region: SWIC
Location: Albuquerque, NM
Vehicle:
2006 WRX Limited Wag
9.9@142

Default

Try a stock BPV. If yours is leaking under vacuum it will cause your issue. You don't have to keep the stock one, just use it to troubleshoot. I had a similar problem on an 05 STi because the owner had left the fuel pressure regulator vacuum line disconnected. The other thing you need to check is that the recirc line that you are no longer using is properly plugged.
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Old 11-21-2007, 06:51 PM   #3
bboy
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Join Date: Mar 2004
Chapter/Region: NWIC
Location: Seattle, WA
Vehicle:
04 Improved STI
Dirty White

Default

There are no signs of a vacuum leak, but I can have him check again. The BOV is a concern it's not one where you can easily cup it to see if it's leaking. I asked him to run without one and see if it still stalls. Additionally I told him at a minimum to inspect his MAF to see if it's dirty.
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Old 11-23-2007, 05:40 PM   #4
kingtut12
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Join Date: Feb 2005
Location: Louisville, KY
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2002 2.5 WRX BY
RIP 02' 2.5WRX PSM

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This is an identical problem I had on an older WRX of mine. It never happened until I went with an atmospheric BOV. I know you didnt want to hear that - but I just wanted to share my experience.

BTW, the problem went away when i went back to a recirc. valve. GLuck.
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Old 11-27-2007, 04:04 PM   #5
bboy
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04 Improved STI
Dirty White

Default

It was the BOV. It would stay open, then eventually close. Changing to recirc cured the problem.
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Old 11-28-2007, 11:10 AM   #6
06rexwagon
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Join Date: May 2006
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Location: Albuquerque, NM
Vehicle:
2006 WRX Limited Wag
9.9@142

Default

Hate to say it but we told you so. Glad it's all worked out.
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