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Old 11-26-2022, 11:28 AM   #1
JohnSub2013Sti
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Default Rough idle (bouncing) and stalling 2013 sti

I recently rebuilt the motor on my 2013 subaru sti. The vehicle runs and sounds good, but it idle bounces up and down +/- 350 rpm. It will then proceed to stall (after its up to temp and the revs are at idle speed). This only happens when there is no input to the throttle. If you're on the throttle even a little the problem isn't there.

I've already checked the obvious. The coils and spark plugs are new. And there's no vacuum leaks.

I have cel P0336 which is crank position sensor A circuit range/performance. I believe this is just a faulty sensor (ordered one already). But I don't think the sensor is the underlying problem.

I was wondering if anyone has had something similar happen to them. Or would have input for this.

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Closed Loop Fueling
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Last edited by JohnSub2013Sti; 12-02-2022 at 01:15 AM.
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Old 11-28-2022, 03:25 AM   #2
alexmartynyuk
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If the ecu isn't getting reliable data from the crank sensor the ignition timing will be all over the place which can cause stalling and idle speed to bounce around. Fix the issue, if the idle issue still exists its possible that there is something else going on. Seeing datalogs would definitely help.
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Old 11-28-2022, 03:03 PM   #3
JohnSub2013Sti
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Thanks for the feedback, I have limited info in terms of data logging
AFR Learning 1 A: 4.6%
MAF: 2.5 - 4 g/s
IAM 0.5 (I did a reflash and as this is a new short block with an issue it hasn't been driven, just started in the 1000-3000 rpm range to diagnose, was brought up to temp a few times) (I'm assuming it hasn't had a chance to go to 1 or this is bc of the crank sensor?)

I did order a new crank sensor that will be installed on Friday. What you said makes sense.

If the issue persist what would be useful in terms of logging data?
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Old 11-28-2022, 08:40 PM   #4
Subie_
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Quote:
Originally Posted by JohnSub2013Sti View Post
Thanks for the feedback, I have limited info in terms of data logging
AFR Learning 1 A: 4.6%
MAF: 2.5 - 4 g/s
IAM 0.5 (I did a reflash and as this is a new short block with an issue it hasn't been driven, just started in the 1000-3000 rpm range to diagnose, was brought up to temp a few times) (I'm assuming it hasn't had a chance to go to 1 or this is bc of the crank sensor?)

I did order a new crank sensor that will be installed on Friday. What you said makes sense.

If the issue persist what would be useful in terms of logging data?
If you really really think it's a sensor issue, a pocket oscilloscope off Amazon can confirm it.
It's pretty legit, especially if you need to read squarewave. I have the DSO213. It's a cheap little one, but it works great - reads & records crank & cam signals, injector pulse, etc... it's a nifty tool to have in the box.
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Old 11-28-2022, 09:24 PM   #5
JohnSub2013Sti
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I'm more hoping it's the issue its definitely something the needs to be fixed either way

This is what i did to the motor:
It was a shortblock rebuild. So a new crank (oem) nitrided, manley forged pistons and rods (Stock compression), king racing rod and crank bearings. New water pump, new 12mm oil pump, new timing kit (Timing thoroughly checked on install).

I'd be open to alternative conclusions if you have any. && Thanks for the suggestion maybe this could be a future tool
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Old 11-28-2022, 09:24 PM   #6
JohnSub2013Sti
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I'm more hoping it's the issue its definitely something the needs to be fixed either way

This is what i did to the motor:
It was a shortblock rebuild. So a new crank (oem) nitrided, manley forged pistons and rods (Stock compression), king racing rod and crank bearings. New water pump, new 12mm oil pump, new timing kit (Timing thoroughly checked on install).

I'd be open to alternative conclusions if you have any. && Thanks for the suggestion maybe this could be a future tool
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Old 12-02-2022, 01:17 AM   #7
JohnSub2013Sti
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Update on this. I ordered the wrong crank sensor. So I have the correct one arriving tomorrow

I also added logs to the main post if this would tell anyone something. I would greatly appreciate any input.

Thanks for everyone's help so far
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Old 12-02-2022, 01:17 AM   #8
JohnSub2013Sti
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Update on this. I ordered the wrong crank sensor. So I have the correct one arriving tomorrow

I also added logs to the main post if this would tell anyone something. I would greatly appreciate any input.
Some of the logs are very long the general logging profile in particular. As they were from cold start until the car stalled

Thanks for everyone's help so far
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Old 12-02-2022, 05:13 PM   #9
JohnSub2013Sti
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Crank sensor didn't fix the problem
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Old 12-03-2022, 09:04 AM   #10
JohnSub2013Sti
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There was a broken tooth on the reloctor ring of the crank sprocket. I must of droped it during the rebuild idk.

I don't have a new one yet

Sent from my SM-S901W using Tapatalk
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