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Stalling Subaru

2003 Subaru Forester automatic non-turbo. Vehicle stalls out at long red lights. No sputter, shudder, or warning. Idle just drops to zero. May happen twice in one day or once in two or three months. No rhyme or reason. Runs great otherwise. No drivability issues until I am stopped. I replaced the idle air control (IAC) solenoid valve last week and thought I cured the problem. But the vehicle cut out on my wife while she was stopped, waiting to yield into traffic this evening. I am at my wit’s end.

I’ve seen this on other (non-Subaru) cars: The “crank angle sensor” could be intermittent. This tells the distributor-less ignition to fire the proper cylinder, at the proper time.

Are any codes thrown? When it stalls, does the dash light up or does it go dark?

Ther are no codes. No CEL. The normal dash lights are lit when it stalls. Oil, battery, ect. And it will start right back up as if nothing was wrong. That’s the part I can’t figure out.

The crank sensor could cause stalling but that would throw a CEL.
I’m not sure whether the car will throw a CEL when the main relay is intermittent. It pretty much turns everything off (injectors, etc) on a Subie. I’d look in that direction.

Subaru main relays don’t fail very often (unlike Hondas) but perhaps check the wiring near it, make sure it is seated well, etc.

Even though there was no CEL, I rescanned the vehicle. This time it showed P0335. Crank shaft potition sensor. I’ll be ordering one and get back to you. Just seems odd it only happens at a complete stop.

Ah, okay. Well, that’s very likely your cause. Yes, you won’t always see the light turn on when a code is thrown.

Hopefully the new sensor will correct the problem. If you still have trouble then I would check to see if there is a vacuum leak in the brake system.

Perhaps the reason it only happens at a complete stop is that when the engine is cranking along at a few thousand rpms the crank simply “blows by” the intermittancy, assisted by the inertia of the 3000 pound flying object (the car), refiring before the symptom is noticed. Whereas at idle, the intermittancy in the signal is enough to allow it to shut down completely.

You’re headed down the right road. Let us know how you make out.

Been away for a while. Replaced the crank position sensor this morning. Wife states the RPMs don’t dip down as low when coming to a stop. Will run er for a week and get back.

@Get-aTrek thanks for the update.

And good luck!

One week down and no problems. Looks like the crank position sensor did the trick. I wish I had replaced the $35. part first instead of the $365. IAC. Unless you hear from me again, we can put this one to bed.

Very nice. Thanks for the update.
I wish you had replaced the $35 part as well - it would have left you a grip of cash to buy us all a round with.

@Get-a-Trek by the way, how do you know for sure there were never any stored fault codes?

Just because the check engine light isn’t on doesn’t mean there aren’t any stored codes.
At my shop, I’ve retrieved many stored crankshaft position sensor codes from intermittently stalling GM trucks. In many cases, the check engine light was never on. Some of my colleagues were thrown for a loop and had never bothered to hook up a scanner.