My 2015 Forester idles poorly, can it be adjusted to idle smoother?

Asked by David Feb 14, 2016 at 09:33 PM about the 2015 Subaru Forester 2.5i Limited

Question type: Maintenance & Repair

Ever since I have owned my 2015 forester it has idled poorly, it feels like it misses.  I took it t0 the dealer but hey say it is normal.

11 Answers


Flat fours are not nearly as smooth as a lot of other car engines. Try another dealer as some are not very good but call ahead and run it past the service manager.

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When the CVT is engaged (drive or reverse) the idle drops as the engine is bogged by its frictional losses. So it'll feel rougher than in neutral or park. But if you can't maintain 600rpm min in gear I'd get Subie involved to check the idle control valve.

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Does your Forester trip a code ? My 2014 Idles rough also, dealer said it's normal. Not true, I had a 2010, have a 2014 and a 2017. They all idle smooth except the 2014. The first 2 years it ran smooth then for no reason it started idling rough. It does not trip a code so unless the dealer has a mechanic that is a good trouble shooter or the dealer is willing to spend a little time on it they just simply say it's normal. I am thinking of disconnecting the battery to reboot the computer and go back to default settings.


Check for mysteriously-fouled plug; lost timing chain tension?

Thanks for your reply. I will bring it back to the dealer for another try. I will also mention your response.


If you continue to bog badly or stall intermittently suspect the the CVT too, unfortunately.

my dealer checked my 2015 Forester and found that it stored Code P300 and ordered, per TSB07-112-16r(Technical Service Bulletin) a replacement alternator and pulley. This is supposed to cure my rough idle. We will find out next week if this is the fix. Luckily I have Certified $100 deductible because this is an expensive part.


Great pickup, HN. Why is it all these weird problems are only with the Japanese production Fors and Imps? That said, low idle RPM when the CVT is engaged does slightly shudder all 2.5i, but it's less egregious than in earlier eras.


BTW, rebuilt alts are usually only about $125; plus that aux pulley.

Somewhat recently my 2015 has been idling rough not terrible but annoying and I've owned several Subarus with the same engine. I've had an issue with the battery in this car and I'm not sure that it was Subarus fault under the circumstances. The interesting thing is when I installed a brand-new battery the problem disappeared don't know why little bit beyond my understanding.


At low idle the alt output is too low to maintain smooth running so relies on the too-weak OE battery to help. Better battery helps immensely.

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