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Engine stalls at idle -- but only after long drives

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Model: 2013 Subaru Outback
Engine: 2.5L
Transmission: Continuously-Variable (CVT)
Mileage: 99,000 on chassis, ~10k on new short block (replaced Nov. 2018 for free due to Subaru's oil burn issue)
Issue: After long drives, the vehicle will sometimes stall at idle.

I'm having an odd problem with my 2013 Outback. It seems that after a long drive, the engine will sometimes stall out at idle speeds, but only after a restart. I don't have any problems at all during the actual long drive, but after getting home, parking, shutting it off, and then turning the engine back on within 5-10 minutes or so, the engine will stall out at idle.

Shifting into P, R, N, D all work fine. If I shift into N as I roll into a stop sign and keep the revs high, the engine does not stall out. It will stall if I allow the revs to drop down to normal idle RPM.

All fluids look fine. Engine radiator cap is not abnormally hot (although the car does not have a coolant temperature gauge, only an idiot light. The idiot light did not come on.)

There are no dash lights. No check engine light. No engine codes stored in memory, per my OBD-II reader.

Even more bizarrely, the problem seems to resolve on its own after 10-15 minutes of cooldown.

This issue happened once, after a long drive in March 2019, and then did not recur again until today, Jan. 26 2020.

My theories / questions:
  • Could this be an issue with the engine's deliberately-idle-at-higher-revs-until-warmed-up behavior? I know the engine is programmed to idle at higher revs when the engine is cold, and then drop the revs once it's up to speed. Since I only have this issue once the engine is already hot (after a long drive), I wonder if it could be an issue with that system.
  • Possible bad torque converter? (There was a TSB published for the torque converter back in January of 2014 for the automatics with extremely similar symptoms. But I'm not sure if the CVT even has a torque converter.)
  • Is the problem temperature-dependent, or am I being fooled?
  • Possible dirty / contaminated engine air flow sensor?
  • Bad gas?
  • Vacuum leak? (But a vacuum leak wouldn't resolve itself)
  • spark plugs? (But this would cause engine trouble at any speed)
  • Compression problem? (Hope not...)
  • Leaking EGR valve? (again, hope not...)
  • Air filter clogged? (Unlikely, just replaced w/ last oil change)
  • Leaking head gasket?! (super hope not, short block was just replaced a little over a year ago for an oil burn issue, and the car has no other symptoms, and there's no sign of coolant in the oil).

Would love to hear your thoughts. Thanks.
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2020 Onyx
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If you're talking about a 2006 Outback 2.5 listed in your account, it does NOT have direct injection. Please folks when you talk about an engine problem, specify exactly the year, trim, engine, transmission, etc. Many people complain about "the same thing" for different engines and they aren't necessarily the same thing. In some models, the torque converter might stay locked up, in another model that's not a typical issue. Details matter so if you want any help please provide every single detail you can about your problem.

If you changed parts, which parts exactly and what did you replace them with (brand, source)? What was the sequence of things you tried with the car and did any of them make any difference? Was anything changed prior to the problem developing (e.g. I had just taken a trip to Colorado, my car hadn't run for 6 months, driving 5 miles daily with no problems for that past year then suddenly). Did the problem happen all at once, or was it gradual deterioration? If you changed spark plugs give the exact model and what gap you set them to. Every single detail might matter. Don't wait for someone to ask you every single detail like a 20 questions game. Spill the beans - all of it. Are you the original owner since new? Did you just buy the car yesterday? WHAT IS THE ENTIRE SITUATION?

If it's a problem with stalling or maintaining an idle that is a common problem for any gas engine but the details vary depending on which engine it is.

Something like BG44K works well to clean fuel injectors and unless you suspected something else, that would be a reasonable thing to try.
 
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I have a 2010 Impreza Outback Sport with an automatic transmission. I currently have 116,000 miles on it. About 2 months ago it started stalling at idle.

When it is cold it will run perfectly. I can drive it around town (with many start and stops) or on the highway. After about 30 minutes when I come to a stop it starts to shake and will eventually stall.

When stopping I put the car in neutral but it still stalls so I do not believe it is the Torque Converter as well as brought it to a transmission shop and they told me it is not as well.

I turned the A/C off to rule out a malfunctioning compressor. It still happened.

I have noticed that on the morning drive to work (about 6am) I make it to work (about 30 miles) without an issue. In the afternoon (about 5pm) which have been extremely hot if I hit any traffic on the highway I barely make it home (if I actually make it). Once the stalling happened a few times I can no longer put the car in drive without it stalling immediately. I have to wait at least a half hour for the car to cool to restart the car and pray I make it home.

I have changed:
Spark Plugs
wires
coil pack
EGR value
timing belt/water pump/ thermostat
MAP sensor
A/C belt
Alternator belt

I cleaned:
the MAF sensor
throttle body

Anyone with any info on what I should try next I would appreciate. I'm not a mechanic and out of ideas.

Thanks
 

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2020 Onyx
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A stuck open PCV valve could cause it, or a cracked vacuum hose that tends to open up when it gets hot.

No codes from a scan tool?

Did this problem develop gradually over time or did your car just start suddenly misbehaving when hot?

I assume you did all of the above replaced parts after the problem started and none of them made any difference?
 

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A stuck open PCV valve could cause it, or a cracked vacuum hose that tends to open up when it gets hot.

No codes from a scan tool?

Did this problem develop gradually over time or did your car just start suddenly misbehaving when hot?

I assume you did all of the above replaced parts after the problem started and none of them made any difference?
Sorry …. I forgot to mention that I’m not getting any codes at all on the dash.
Yes it started suddenly one day and it was raining out. That’s why I started with the wires/plugs/coil pack.
And yes it was all done after the problem started.
 

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2020 Onyx
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I'd look for vacuum leaks because while the engine is cooler it runs richer and as it heats up it runs leaner (generally) and a vacuum leak might tip it over to just too lean. A stuck open PCV valve or a cracked PCV hose could do that, and cracked hoses can leak more when they get warm.

Some electronic things also work less well when they get hot due to increased resistance, so you could check all your engine grounds, for example the ones that connect the heads to the chassis, the transmission to the firewall, etc.
 

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I'd look for vacuum leaks because while the engine is cooler it runs richer and as it heats up it runs leaner (generally) and a vacuum leak might tip it over to just too lean. A stuck open PCV valve or a cracked PCV hose could do that, and cracked hoses can leak more when they get warm.

Some electronic things also work less well when they get hot due to increased resistance, so you could check all your engine grounds, for example the ones that connect the heads to the chassis, the transmission to the firewall, etc.
Ok thanks for the tips. I will update when I get to start checking these things.
 

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2006 Outback 2.5, manual transmission
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I had the same problem. Idles fine when cold, rough and stalls after the engine is hot. No CEL light.
After cleaning the MAF sensor, MAP sensor, EGR valve and throttle body (twice), replacing the upstream O₂ sensor (downstream previously replaced), then decarbonizing the intake manifold (twice, using CRC intake valve and turbo cleaner), sprayed carb cleaner on all vacuum hoses and their connections, I gave up and took it to my mechanic.
The mechanic diagnosed it as a bad throttle, while also stating that "throttles rarely go bad". If my other car was working, I would have paid a visit to a local scrap yard to pull 2 used throttles (2006-08, most Subaru models, so they should be abundant) but I didn't. They installed a new $750 throttle.
It DIDN'T fix it!!!
I took it back to them and they replaced the ignition coil - the one (NGK) I installed to replace the one ("economy favorite at RockAuto) I installed to replace the original coil, which had a cracked housing on one of the wire connections. They installed a Beck Arnley coil (the only aftermarket brand they trust) and it seems to have fixed it. No trouble after two 1/2 hour drives and two 2-hour drives. Idles correctly now.
 

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Just to post an update …..
I finally brought it to a mechanic that had the right equipment to diagnose the problem. It ended up being a bad ignition coil. I replaced it several months ago but it was an aftermarket one that apparently the car didn’t like.
The mechanic replaced it with an OEM one and the problem has seem to go away.
 

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Sorry to revive this old thread but I just had the same exact stall at idle after warm restart issue after a long thanksgiving day drive. Same 2013 outback fb2.5 as the original poster. i gave it a tiny bit of throttle after starting and was able to keep it from stalling. Then drove with no issues except long term fuel trim at idle went up to 7-10 (but come down to normal above idle). No cel, pending codes or obvious vacuum leaks. How does one diagnose faulty ignition coils as suggested in the last post?

Edit: after thinking about it some more, my suspicion is possible vapor lock from heat soaked engine after parking for 15mins following a multi-hour drive in 60degree ambient with winter blend fuel.
 
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