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Discussion Starter #1
I Have a 2015 WRX that I bought Pre-Certified with 16K miles. I plan on doing some upgrading but I need to figure out this problem first.

The car stars fine, warms up fine, but when it settles down into a resting idle (700RPM) it seems a little rough. I'm using 93 Octane.
Every second or so, but not regularly spaced out, the engine gives a little "bump". With the hood open you can see the engine move a little when it happens.
Under normal driving conditions the car is fine, no misses, backfires or knocks. I will add though that it has tried to stall on me about 3 times.
Once when I was doing some long steady driving. I had it on cruise control doing around 65 in 5th most of the time, no heavy pulls or turbo use.
Came to a few stops here and there, but at one light the rpm's starting dipping out and the ECM would compensate and bring it back up, repeat. It did it again later the same night.
No CEL, the water temp was fine, no knocks, no smoke, nothing unusual but the idle. The other time was a few days later under normal "city" driving conditions. Tried stalling again, but was fine except for the idle.
It's still under warranty so I had it looked at by the dealership, and they couldn't find a problem.

The only thing i've done to this car has been replacing the most of the intake and charge clamps. This is a pretty simple thing, and the idle was the same before and after.
And yes, because I know it will be suggested, I can go back and check the clamps. No big deal, but im pretty sure I installed them right. And I also inspected the intake ducting for cracks or holes, its fine.
The MAF and neutral switch had to be replaced a few days after I bought the car, but the switch seems to be a somewhat common issue, and the I think (im not sure) the previous owner used an oiled air filter and messed up the MAF. But I'm not sure. Both of these problems occurred simultaneously.

At this point I'm thinking it could be a few things.
1. Fouled spark plugs. Not looking forward to checking these.
2. Bad Ignition coil. Though I think this would throw a CEL.
3. Vacuum line problems. I want to know which ones are directly responsible for idle and inspect them. Maybe there's oil from the turbo in them, just enough to choke them?

I'm open to suggestions and thoughts. I'll try to provide any info needed to help you help me. Thanks!
 

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does the 2015 WRX have the recall like the 2016 did for possible cracked intake tube. In the Symptoms description for the 16' they said could cause rough idle or stalling.

I never had the issue, but they replaced mine under warranty because it fell in the serial # range.
 

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Hey,

I just got my car back from the dealership on Friday for this same issue ('16 WRX M/T). When idling the RPMs would drop and it would start to shake and the engine would give itself a little gas to raise the RPMs then the cycle would continue to repeat. At one point it threw a check engine P000A code but that was after it was doing this intermittently for a while. The dealership replaced the camshaft solenoid, they said it had an internal electrical shortage. Since I got it back, so far so good.
 

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Discussion Starter #4
does the 2015 WRX have the recall like the 2016 did for possible cracked intake tube. In the Symptoms description for the 16' they said could cause rough idle or stalling.

I never had the issue, but they replaced mine under warranty because it fell in the serial # range.
No recall for this one involving the intake. It was made later than the ones that were. I already inspected the intake ducting for cracks or leaks and found nothing.
 

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Discussion Starter #5
Hey,

I just got my car back from the dealership on Friday for this same issue ('16 WRX M/T). When idling the RPMs would drop and it would start to shake and the engine would give itself a little gas to raise the RPMs then the cycle would continue to repeat. At one point it threw a check engine P000A code but that was after it was doing this intermittently for a while. The dealership replaced the camshaft solenoid, they said it had an internal electrical shortage. Since I got it back, so far so good.
Was it idling rough before it started to stall? Or was it smooth, and just tried to stall out of nowhere? Thanks for the input, this could possibly be the case, but until it throws a CEL I have to check other stuff that wouldn't. At this point a CEL would be welcome.
 

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Mine didn't stall at all. It would be smooth when idling then out of nowhere get rough and almost stall because the lights would dim and it would shake hard but the RPMs would kick up to make it feel normal again then it would repeat this process over and over. My '15 Legacy had an issue with it stalling though. It would turn on then out of nowhere stall out. They had to replace the fueling system, something in it wasn't allowing the engine to receive enough gas consistently to remain on.
 

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There was a TSB for the ECU for the My15, and depending on the build date, a recall for the ECU for a reflash due to pre-ignition detonation. I would look in to that, The Subaru Dealership should have the work on file if it was performed.
 

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There was a TSB for the ECU for the My15, and depending on the build date, a recall for the ECU for a reflash due to pre-ignition detonation. I would look in to that, The Subaru Dealership should have the work on file if it was performed.
I checked with them about that. Their records show that the TSB for the ECU was installed back in January, for the pre-ignition problem. I'm up to date as far as any ECU patches are concerned.
 

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Mine didn't stall at all. It would be smooth when idling then out of nowhere get rough and almost stall because the lights would dim and it would shake hard but the RPMs would kick up to make it feel normal again then it would repeat this process over and over. My '15 Legacy had an issue with it stalling though. It would turn on then out of nowhere stall out. They had to replace the fueling system, something in it wasn't allowing the engine to receive enough gas consistently to remain on.
Ok. Sounds like its not quite the same problem i'm having.
I'm not getting any shaking or major stall issues (only tried to stall 3 times in the last 2800 miles), just the idle is a little rough and should be smoother. I'm not saying it couldn't be, but it sounds different than my issue.
 

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Discussion Starter #11
I believe I recall someone else had this issue and used Sea Foam to correct the issue.
I have a bottle of Berryman B12 Chem Tool, I'm assuming its quite similar to Sea Foam.
I can try using the recommended amount in my fuel ( and no, im not gonna suck it through the brake boost line ) to see if that helps clear it up. Thanks.
 

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Discussion Starter #12
Put some B12 in my gas and filled the tank, nothing changed yet.

I will add this though : When I put the car in gear at a light, and the RPM's climb to ~750-800, the rough idle completely stops. I think this car does not like idling at 700 RPM's. Either it's too low, or its not receiving enough gas at 700. I don't know if they (FHI) did this to squeak out better mileage, but I dont like it. All manuals I drove before all this EPA crap was popular, idled at an even 1K RPM's and never had these problems.

Yet again, this sounds like another stock problem that a Cobb V3 will fix. I would really like my idle to be about 800 RPM's minimum.
 

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I had similar issues. With a/c on it would actually stall at idle. Took a while to throw a code the the cam sensor was replaced. That was probably 15k ago and pre stage 2+. Once it throws a code take it in.


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I am New to this forum thing, but I need some help. I have an 06 wrx sti and at idle and while in gear driving the rpms will bounce up and down about 800. While driving it causes the car to accelerate and slow down over and over very evenly. I have been trying to trouble shoot it for weeks now
 
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