Intermittent Stalling Issue

[The Critic]

2014 Forester 2.5, 125K. Driver complains of an intermittent stalling issue - it happens about once every other month. The stall occurs at idle. I have never been able to duplicate the concern.

Fuel trims are normal (+/- 5%), oil level is correct and there are no stores fault codes that are relevant to the concern. No obvious issues were found during the visual inspection.

My only abnormal finding was the throttle body- it is abnormally dirty:

So, I cleaned the throttle body and performed the idle relearn procedure. We’ll see if the issue returns, but I wonder if this was the issue.

 

[The Lube Guy]

My only abnormal finding was the throttle body- it is abnormally dirty:

That was my first observation as well. Does this engine have an EGR valve? What about an EGR cooler?

My logic is that oil vapors, unburned fuel, and water vapors are making their way into the intake. Combined with the inert gases from the EGR, this can cause significant dirt buildup. Short trips will exacerbate the problem.

 

[t1snwrbrdr12]

I worked at a Subaru shop until 2013. I’m no Subaru expert but we had to clean the throttle plates a lot extremely low idling and stalling when they went throttle by wire. I think you did good.

 

[GSCJR]

I think you did good.

+1

 

[mt23]

kudos to cleaning the throttle body. I recommend cleaning the egr valve as well. I've noticed several FB engines stumble at idle especially during warmup solved by cleaning the egr valve.

 

[The Critic]

I worked at a Subaru shop until 2013. I’m no Subaru expert but we had to clean the throttle plates a lot extremely low idling and stalling when they went throttle by wire. I think you did good.

I was surprised by how heavy the buildup was. This engine burns 1qt/2500 miles.

 

[Brons2]

excellent cleaning job, looks like a new part

 

[burbguy82]

Would perhaps a catch can be in order?

 

[meep]

We just traded our ‘15CRV. It’s had a chronic stumble/hesitation with occasional hard stall for a while, mostly minor but in recent months increased in frequency. ATF change reduced a rattling sound, which then got loud again. New plugs changed the feel of the hesitation, but then continued increasing. No codes. I started wondering if they weren’t all related to the CVT. We bought it used with an unknown history. Read the writing on the wall and traded it in. All that to say, don’t overlook the transmission.

 

[t1snwrbrdr12]

View attachment 222056
I was surprised by how heavy the buildup was. This engine burns 1qt/2500 miles.

If I remember right Subarus were occasionally plagued by lazy responding oxygen (or did they call them air/fuel?) sensors. But I think those problems were with older models than you’re working on.

 

[ka9mnx]

Does this engine have the old IAC or is the idle computer controlled? EGR could be sticking open too, if it has one.

 

[Marcozi]

Did you scan the engine computer for codes?

 

[zzyzzx]

It needed that cleaning anyway.