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Beyond frustrated with unstable idle and surging in neutral


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I'm not really sure what it is! That's why I am so interested in this thread.

 

Doesn't happen all the time, and when it does, it's only when I press the clutch in. I'm hitting peak boost according to my gauge and verified with AP.

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I emailed IAG earlier today asking what other tests Cleo performed to narrow things down for further troubleshooting. They said he also performed a smoke test which showed no vacuum leaks and did a series of tests with the car in closed loop and open loop.

 

Cleo mentioned that another likely cause was the Cobb XLE was not closing/opening properly. They advised to look into this now so I just ordered a Tial Q. I hope to have it by Thursday and on the car before the weekend. Fingers crossed this takes care of the issue.

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When it surges, does anything change in your Req. Torque (N-m) parameter, or Throttle Pos. (%)? Are you running the stock FPR? I'm guessing your A/F Sens 1 Ratio (AFR) is bouncing around since the front o2 sensor was suspect?
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Cleo mentioned that another likely cause was the Cobb XLE was not closing/opening properly.

 

Like it's not a good BPV for the car or you have a bad unit? Islandborn is a Coob groupie, is he running the XLE?

 

 

Are you VTA or recirc?

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When it surges, does anything change in your Req. Torque (N-m) parameter, or Throttle Pos. (%)? Are you running the stock FPR? I'm guessing your A/F Sens 1 Ratio (AFR) is bouncing around since the front o2 sensor was suspect?

 

I have plenty of datalogs that I could send you if you'd like. If so, please provide an email address.

 

Like it's not a good BPV for the car or you have a bad unit? Islandborn is a Coob groupie, is he running the XLE?

 

 

Are you VTA or recirc?

 

Both I guess. Cleo said he's seen a few Cobb units failing lately and suspects mine is not functioning properly.

 

I'm speed density so running VTA.

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Looks to be fuel related, from a few things: Your IDC drops, which causes you to run lean, which is shown in your logs and maybe why they thought your o2 sensor was bad. This also seems to then raise your RPM's, to increase your IDC, which then adds a bit too much, causing you to run rich. Based on that cycle. I would have your FPR checked out, as well as adding your fuel pump to your logs, to rule that out as well. Just a few ideas and observations.
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Looks to be fuel related, from a few things: Your IDC drops, which causes you to run lean, which is shown in your logs and maybe why they thought your o2 sensor was bad. This also seems to then raise your RPM's, to increase your IDC, which then adds a bit too much, causing you to run rich. Based on that cycle. I would have your FPR checked out, as well as adding your fuel pump to your logs, to rule that out as well. Just a few ideas and observations.

 

Many thanks for taking the time to look over it.

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I did not read the entire thread...

 

Rather than throw out random "have you tried this" shots I will try to ask questions that can lead to uncovering the issue. Obviously I cant inspect the car myself and must rely on the provided data. For now, as the issue did not arise for some time after the initial tune I must "assume" we are looking for a mechanical/sensor issue.

 

A shop performed a smoke test and there were no leaks found. So, what is the current idle RPM set at? Is the motor built? What O2 sensor did you use when you replaced it (brand/style)? In your SD tune, is your tuner using the MAF signal for anything (including IAT) and is it a hybrid tune? What BOV/BPV are you running? What fuel pump and FPR are you running? What is your idle fuel pressure?

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I did not read the entire thread...

 

Rather than throw out random "have you tried this" shots I will try to ask questions that can lead to uncovering the issue. Obviously I cant inspect the car myself and must rely on the provided data. For now, as the issue did not arise for some time after the initial tune I must "assume" we are looking for a mechanical/sensor issue. Yes, this seems most likely.

 

A shop performed a smoke test and there were no leaks found. So, what is the current idle RPM set at? 800ish RPM Is the motor built? No, 100% stock What O2 sensor did you use when you replaced it (brand/style)? Subaru OEM In your SD tune, is your tuner using the MAF signal for anything (including IAT) and is it a hybrid tune? Don't think so, pretty sure it's full SD What BOV/BPV are you running? Cobb XLE 100% VTA What fuel pump and FPR are you running? DW300 pump, OEM FPR What is your idle fuel pressure? Don't know at this moment

 

Thanks Mike!

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800rpm is "fine" on a stock long block. If built or running aftermarket cams raise that to 1000rpm.

 

Stock O2 sensors should not be an issue. But not a bad idea to verify the sensors are operating properly. If the upstream O2 is not, this could cause your issue.

 

If full SD even a leak should not cause a this. So, venting to atmosphere is not an issue.

 

Check your fuel pressure. Check your fuel pump duty and voltage (and amp draw if you can). If fuel pressure is modulating rather than steady this can deff cause your issue.

 

If you are true SD, I would lean towards a fueling issue. Just recently I found a fuel pump housing cracked (upon removal from the tank). The crack was the cause of the droppping fuel pressure, hunting idle and scary lean conditions under WOT.

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On the current map, fuel pump duty was either 33 or 67 on the casual drive to work this morning. It seems there are not any major fluctuations here. I will flash the original map tomorrow morning and see what fuel pump duty looks like again.
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  • 1 year later...

I am a little late to this, and may not have anything useful, but I am curious...

 

Have you monitored your AVCS in/out/left/right ? And, what do you see?

"It's within spec" - SOA :rolleyes:

"Depth is only shallowness viewed from the side." - Fredism

"So, how much did it cost for your car to be undriveable :lol:." - Stephen (very close friend)

"You have done so much it would be stupid to go back." - Sunny of Guru Electronics

 

2018Q50RS | 2015WrxThread | Shrek

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IAG's final conclusion was that the tables needed to correct the issues at cold start are not available for 5th gens like they are for other Subaru models. No idea what caused this issue to pop up 2-3 months after tuning it with ETS manifold and twin EWGs. Install and tuning was done December 2014 and idle issues popped up in February or March 2015.

 

They were able to get the idle under control by adding a MAF sensor and hybrid tuning the car. It was full speed density before.

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