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Old 09-27-2021, 01:27 PM   #1
Bigwrm
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Default Rough idle with occasional stalling after warmup, logs included.

I've been reading threads for days attempting to chase down this issue. During warmup, idle and parameters all look good but afterward idle gets rough and often stalls after pushing in the clutch at highway speeds. I changed the air filter and cleaned the MAF sensor, it didn't help. It almost seems like a vacuum leak after warming up. I notice the TPOA stays the same but the MAP moves around and the AF sensor reads lean. What seems strange to me is how long it takes for the system to go back to closed-loop at idle. Romraider tune has run perfectly for over 100,000mi. Logs are posted below.

https://drive.google.com/file/d/1Ped...ew?usp=sharing

https://drive.google.com/file/d/1Mi6...ew?usp=sharing

05 Forester XT, IAG AOS, Walbro 255, stock injectors, VF39 IWG, TurboXS FMIC with stock recirc valve, Perrin intake, PNP stock headers, Invidia catless downpipe.
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Old 09-27-2021, 02:22 PM   #2
benflynn
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My experience is that it stalls and searches for idle when the idle area is lean. Id suspect the MAF and o2 of all else is same. FYI I run a 06 sti merpmodded ecu in my 05 fxt mt. In case ur also mt and want flex and launch control and such. You loose egt tho.
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Old 09-27-2021, 03:19 PM   #3
Bigwrm
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I may go ahead switch out both but if I could get some feedback on what someone else sees in the logs I'd be very appreciative. I feel like there's something I'm missing. I may go Merpmod after my rebuild next year. I've already got an FP Green for that build.
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Old 10-05-2021, 12:26 PM   #4
GeoNV
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I've been trying to diagnose a similar issue- I notice yours has a lot of similarities to mine- right as the idle speed drops I see that your ignition total timing goes up into the 20's. Mine seems to idle best around 8-12 and starts to stumble when the timing goes into the 20's. some ECU's have idle timing tables defined, but mine doesn't. changing the cruise and non cruise timing tables makes no difference to mine. Look under Alpha idle control and see if you have anything defined there. I notice it's worse on E85 than on 91 octane. My base timing idle doesn't seem to affect this- so clearly more going on in the ECU than what mine has defined.
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Old 10-05-2021, 05:11 PM   #5
SuperPete
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I vote for new MAF, start with that.
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Old 10-05-2021, 05:23 PM   #6
Bigwrm
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I'm not big on throwing parts at it until things work. While it could be the MAF, why would it work fine until the engine has been run for a while. What I find strange is how long the ECU stays in open-loop after the throttle closes and the motor goes back to idle.
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Old 10-06-2021, 01:37 PM   #7
GeoNV
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Are you tuning open source? If so can you post a copy of your tune?
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Old 10-06-2021, 02:15 PM   #8
Bigwrm
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Quote:
Originally Posted by GeoNV View Post
Are you tuning open source? If so can you post a copy of your tune?
Sure, have a look. I haven't messed with the tune in at least 7 or 8 years.

https://drive.google.com/file/d/1N57...ew?usp=sharing

Last edited by Bigwrm; 10-06-2021 at 02:22 PM.
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Old 10-06-2021, 07:50 PM   #9
GeoNV
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Possible the slow return to closed loop is because your CL to OL delay is set to 0.

your idle is still at 700- I found this happened less when I raised it to 900 rpm. it's a bandaid, but maybe it will work.

Have you trolled around on the romraider forums for an answer yet?
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Old 11-21-2021, 11:34 AM   #10
Bigwrm
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Still dealing with this issue. It seems like an intermittent vacuum leak after warm-up. The MAF reading dips and the MAP rises along with the AFR going completely lean.
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Old 11-25-2021, 02:22 AM   #11
STRMfrmXMN
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This might sound dumb, but have you pressure-tested the system to check for vacuum leaks? Rubber has finite life and if you've taken the TMIC off or anything like that recently then you could have opened up a leak. Also, perhaps read this thread from LegacyGT.com. I frequent there and a forum user had a similarish issue to you.
https://legacygt.com/forums/showthre...as-287125.html
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Old 11-25-2021, 08:53 AM   #12
Bigwrm
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I've got it scheduled to be dropped off Monday for a smoke test. The strange thing to me is that the issue doesn't show up until after it's warmed up. My understanding is vacuum leaks are usually found more easily while testing on a cold engine.
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Old 11-25-2021, 04:03 PM   #13
STRMfrmXMN
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Quote:
Originally Posted by Bigwrm View Post
I've got it scheduled to be dropped off Monday for a smoke test. The strange thing to me is that the issue doesn't show up until after it's warmed up. My understanding is vacuum leaks are usually found more easily while testing on a cold engine.
Cold idle is higher than warm idle. You're also running closed/open loop which affects things.

Good luck with your appointment.
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