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Discussion Starter #1 (Edited)
I'm not exactly sure the best way to explain this but I'll do my best. Hopefully you guys can let me know if this is normal or not.

When I'm sitting in the car idling in P, the vibrations from the engine seem very inconsistent. The baseline level feels just about the same as any other car I've ever been in... you can feel it but you don't really notice it. But for about 2-3seconds every 10seconds (VERY rough estimates here) the engine seems to vibrate a little more aggressively (might be better described as "rumbling" at that point). It is noticeable because of the change.

Do you guys experience the same thing or is this unusual?

This is my first Subaru but I was under the impression that the Boxer engine was supposed to be smoother. Per Subaru: "The punch-counterpunch movements of the boxer's pistons cancel out each other for a smoother running engine"

For completeness: This is a 2015 base Hybrid model (although obviously this question pertains to the gas engine) with ~750 miles on it.
 

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This doesn't happen to me consistently, or even frequently, but I do notice occasional moments of engine rumble at idle, when the engine is cold ... and I think a fair number of other people do, as well. My guess is that's a by-product of the ECU hiccuping momentarily as it adjusts the mixture while trying to get the engine up to operating temperature. (It tries to do that quickly, to lessen the pollution the car creates.) In any case, unless it's happening consistently over an extended period of time I don't think it's anything to be concerned about.

Interestingly, I mostly notice the moments of engine roughness after there's been a substantial change in the outside air temperature -- say, a week of cold weather followed by a very warm day. I don't know if the ECU is smart enough to do this, but maybe it was expecting a cold-weather start and got a warm one instead?
 

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Discussion Starter #3
This doesn't happen to me consistently, or even frequently, but I do notice occasional moments of engine rumble at idle, when the engine is cold ... and I think a fair number of other people do, as well. My guess is that's a by-product of the ECU hiccuping momentarily as it adjusts the mixture while trying to get the engine up to operating temperature. (It tries to do that quickly, to lessen the pollution the car creates.) In any case, unless it's happening consistently over an extended period of time I don't think it's anything to be concerned about.

Interestingly, I mostly notice the moments of engine roughness after there's been a substantial change in the outside air temperature -- say, a week of cold weather followed by a very warm day. I don't know if the ECU is smart enough to do this, but maybe it was expecting a cold-weather start and got a warm one instead?
I mostly notice it in the morning just after starting it up. While I'm sitting there fiddling with the bluetooth or deciding what to listen to, etc.

It's hard to say whether or not it continues after the engine has warmed up, because once the engine is warmed up the car will shut it off entirely whenever I stop.

I plan to monitor it over the next week or so. I'll have to monitor carefully to see if this behavior is temperature-dependent.
 

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Yep, that's when I notice it as well ... nearly always within the first half-minute or so after the engine's started. Rarely, if I start driving right away I'll notice it at the stoplight that's a couple blocks from my house, but never after that, and never after a warm start.
 

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Their are manufacturer bulletins out their about hard start, and rough idle. Contact your dealer about bringing it in to have them look at it.
 

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This isn't a case of hard starting though and seems to be a normal result of how the cold (fast) idle works. I wouldn't be surprised if the system is designed to regularly check whether a slower idle can yet be supported to get the idle speed down ASAP for emissions reasons.
 

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Echoing others... it sounds normal to me. Also, don't let the Subaru boxer "punch/counterpunch" marketing get to you too much. Yes the boxer has its advantages, but the marketing arm of any company (including Subaru's) will often overstate the benefits (or at least state them in a way that makes them sound superior to the competition). Subaru balances their engines by using horizontally opposed engines. Their competition balances with other methods (like balancing shafts). Both methods have their advantages/disadvantages and neither is going to be without some NVH.
 
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At cold start, this car sounds and feels like a diesel. Even more than my STi. Once it's warmed up, it's much smoother than my STi.

My STi has always had this off-beat idle from day one even after a Protune by my tuner.

IMO I think it's just the nature of the flat-4 boxer engine.

Just consider it a character trait...the boxer rumble (I realize that's from the UEL exhaust mani of the STi).
 

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Discussion Starter #9
Echoing others... it sounds normal to me. Also, don't let the Subaru boxer "punch/counterpunch" marketing get to you too much. Yes the boxer has its advantages, but the marketing arm of any company (including Subaru's) will often overstate the benefits (or at least state them in a way that makes them sound superior to the competition). Subaru balances their engines by using horizontally opposed engines. Their competition balances with other methods (like balancing shafts). Both methods have their advantages/disadvantages and neither is going to be without some NVH.
Yea I assumed that it was mostly marketing fluff. I was just looking for reasons why it should be at least as smooth as my old beater, not worse.

At cold start, this car sounds and feels like a diesel. Even more than my STi. Once it's warmed up, it's much smoother than my STi.

My STi has always had this off-beat idle from day one even after a Protune by my tuner.

IMO I think it's just the nature of the flat-4 boxer engine.

Just consider it a character trait...the boxer rumble (I realize that's from the UEL exhaust mani of the STi).
If that is the case, I'm fine with just considering it a character trait. I just wanted to make sure it was normal before I decide to ignore it.
 

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Both of my Subies have that "rumble" which makes it feel like the engine isn't as smooth. My Lexus IS 300 with the 2JZ straight-six is the smoothest engine in any car I've owned.
 

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surprised to see that no one has said PZEV yet. The ECU changes the idle/timing/fuel to speed up operating temp. Completely normal. Go for a nice drive and pull over somewhere safe and turn off the ac- see how smooth it is.
 

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Discussion Starter #12
surprised to see that no one has said PZEV yet. The ECU changes the idle/timing/fuel to speed up operating temp. Completely normal.
Isn't it weird that it goes in and out as I sit there? If the ECU is modulating the idle/timing/fuel to do something intelligent, why would it go back and forth?
 

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I already posted my theory, to test whether a lower emissions setting would allow maintaining idle. If it doesn't and stumbles, the ECU steps in and feeds more fuel for a while until it checks again.
 

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surprised to see that no one has said PZEV yet. The ECU changes the idle/timing/fuel to speed up operating temp. Completely normal. Go for a nice drive and pull over somewhere safe and turn off the ac- see how smooth it is.
lol ... hey, that's pretty much what I said! I just left off the acronym. :p
 

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Discussion Starter #15
I already posted my theory, to test whether a lower emissions setting would allow maintaining idle. If it doesn't and stumbles, the ECU steps in and feeds more fuel for a while until it checks again.
I missed that part of your first comment. The "checking regularly" would explain why it comes and goes.
 

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This is my first PZEV rated car. My understanding is that a cold start-up it runs rich to speed up cat light-up for emissions purposes and adjusts once warm.

Is there anything else that the XV tries to speed-up the process at start-up?

I had a VW VR6 that had a stupid fan system that pumped air into the cold engine to improve emissions at start-up. The fans were known to fail causing the "normal" VW check engine light.

My repair in that situation was to buy a block-off plate and stick a piece of black electrical tape over the CE light.
 
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