My 2015 Subaru legacy has been having some issues coming to a stop. The car first stalled after coming to a stop 3 weeks ago and then never happened again until today. The first time it happened once, then I couldn’t start the car until I gave it gas while starting. The problem happened again today as soon as I backed out of my driveway as I switched from reverse to drive. This time I could start the car up again without stepping on the gas. I drove the car around my neighborhood to test it and it stalled every time I came to a stop. Didn’t matter if i braked hard or very gently. I got the car back to my house and took about an hour break. When I started it up again the issue wasn’t as bad but still persisted sometimes. I then tried coasting the car in neutral before coming to a stop and the car never stalled. I drove like this for about 15 minutes. I got to a parking lot where I had to stop and drive very slowly and the car never stalled but did seem a little jerky at times. Afterwards I drove home and had no problems. I stopped coasting in neutral and just stopped like normal and the car never stalled. Doesn’t seem to be any problem going from idle to drive but from drive to idle makes it stall.
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2Check your transmission fluid level. When this happened to me (in an entirely different vehicle), I found that I had a leak in a transmission cooler line and had lost a substantial quantity of fluid.– JakeRobbCommented Jul 10 at 15:38
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@JakeRobb Similar thing happened to me, mechanics.stackexchange.com/questions/89619/…– MonkeyZeusCommented Jul 11 at 16:01
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When you "backed out of my driveway as I switched from reverse to drive" do you make sure that the car has come to a full and complete stop before changing from R to D, or are you letting the shift change the direction of the car? This can definitely damage the torque converter or transmission (Along with drive/cv shafts, U joints, wheel hubs...) which would lead to this problem.– psaxtonCommented Jul 12 at 14:54
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If, however you did come to a full and complete stop and the car then stalled when going from neutral to drive, it could still be a torque converter/transmission issue, but it might also be any of a host of sensors needing cleaned or replaced. Their should be a "check engine" type light indicating the malfunction and you should be able to use a code reader to learn which sensor is causing the troubles.– psaxtonCommented Jul 12 at 14:56
4 Answers
Jupiter's answer is well-founded and I've upvoted it, but you might consider one more possibility: that your lockup torque converter is failing to unlock.
If this is happening, you might feel a lurch or lugging (you called it jerky) as you slow down to a stop. If you have a tach and your torque converter remains locked up, you would also see the RPM fall below the normal idle speed as you slow down to a stop, with the speed eventually falling to zero.
The fact that you can stop in neutral without stalling lends some support to this theory.
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I hadn't even considered this, but believe it is sage advice.– Pᴀᴜʟsᴛᴇʀ2 ♦Commented Jul 9 at 15:57
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The jerkiness is not normal. It felt that way 2 times when I drove it 2 days ago. Never when I was slowing down. Only when I was in the parking lot going between idle and drive a lot. If it normal for this type of problem to occur only sometimes? Like on that day it stopped happening after 15 minutes of driving and yesterday I had zero problems.– eewsCommented Jul 10 at 14:28
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@eews Nothing about this problem is "normal" but certainly it is possible for a lockup torque converter to remain locked sometimes causing a stall when you stop and to work normally at other times.– MTACommented Jul 10 at 22:29
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I would expect to feel the jerking/lurching when shifting to and from drive if the torque converter lockup is locked up.– psaxtonCommented Jul 12 at 15:01
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1Torque converter lockup is most often controlled by a solenoid which has an external connection. I don’t know if this is true of a ‘15 Legacy, but if it is: find it and disconnect it. It’ll set a code and turn on the SES, but if this diagnosis is correct then unplugging the solenoid will stop the problem from happening. (This is only a way to confirm the diagnosis and should not be treated as a permanent solution!)– JakeRobbCommented Jul 13 at 1:00
Two things come to my mind: First would be a bad idle air control valve and\or dirty throttle body. The IAC valve may turn on the check engine light. Second would be a significant missfire which probably would be noticed by a rough running engine and most likely would turn on the check engine light. If this is the case and your check engine light flashes it is not a good idea to continue driving it until fixed. Checking for codes would be a great next step.
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No IAC valve on a Subaru of this era. It's not necessary for electronic throttle cars, which Subaru introduced around 2005. Commented Jul 10 at 7:18
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1Is it normal for any of these problems to occur only sometimes. I drove the car again and had no problems.– eewsCommented Jul 10 at 14:24
Sounds like the engine is leaning-out when the throttle is closed.
In other words, the engine is getting too much air for the amount of fuel metered in.
When you give it more accelerator, you're raising the fuel percentage somewhat.
I suggest you look at all the air hoses, the air filter box, confirm the air filter is there, etc. You're looking for a broken hose, a hole, or a loose connection that is allowing extra air to be sucked into the engine.
Drifting to a stop in neutral separates the wheels from the engine so the engine is idling and not sucking in additional air through the hole as it is back-driven.
I've had something like this with an air ram on top of a wading schnorkel on a vintage landrover. The extra air rammed into the engine while on overrun was enough to lean-out and stall the engine, even when driving at 80 km/h. That was fixed by turning the air ram intake sideways.
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1Good point, if it is a turbo engine (quite likely with a number of Subaru models) then the wastegate solenoid could be malfunctioning and providing too much boost while decelerating.– psaxtonCommented Jul 12 at 14:59
This "stalling" symptom can definitely be caused by the vacuum servo called the "brake booster" having a vacuum leak when the brake pedal is depressed. An experiment to test this would be to start the car, and then depress and hold the brake pedal a few times, at idle. any major change in engine speed points at a vacuum leak. This situation is not uncommon.
