2012 Forester Stalling / Slow Starting

Maintenance/Repairs
1

Hey All,

Thanks in advance for helping out… Ongoing problem, not entirely sure if it’s all related… some of it going on for a long time.

A while ago, 2012 Forester started getting occasionally slow to start. No real rhyme or reason when it was slow and when it was fine.
Change the battery - no change at all to behavior.
Mechanic did the plugs - no change at all - probably a waste of money as the OEMs were iridium I think.
Finally started having some stalling issues. Pretty reliably at cold. Generally when I come to full stop when I first start driving (engine still cold) it will either stall or come close.
Not sure how long it’s been doing this, may be longer than the stalling, sometimes upon acceleration it’ll seem briefly like the pedal is doing nothing and then give me a sudden jolt.
I’ve replaced the airfilter and cleaned the electronic throttle body already - no change.

Got a bluetooth OBD and Torque Pro and logged my commute this afternoon. Attached are some charts comparing a clean stop when the engine was warm (end of the drive) to a near stall just as I was pulling out of work. I think a bunch is just the effects of the near stall but not sure. One thing the got my attention was a fair number of EGR error readings? No codes or warning lights are coming up though. Should that pretty much always be near 0% error all the time? Any chance I just need to clean the EGR valve?

Any other recommendations what I should be logging? Right now I’m logging enough that it’s only updated every 2 seconds (Note… I definitely dropped lower in RPM on the near stall than that data shows - probably just under sampled) - So any recommendations on what’s important so I can limit what I lot and it should increase the update rate…

Any idea?

Scratch that… only letting me attach one image - here’s the long term (30 minute) EGR Errors

Thanks!

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Stalling at the first stop sign of the drive after a cold-engine start is often caused by too lean of mixture and/or too low of idle rpm. Are you able to get a read out of the fuel trims? An EGR problem could cause it, but usually that would also cause a diagnostic code. This seems more likely to be an air leak allowing unmetered air into the engine. Carefully check the air intake path for tears in rubber boots, etc.

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See my 2nd to last reply to myself above, that’s the short term fuel trim on the clean stop vs. the near stall. Also, here’s the long term fuel trim over the half hour commute… looked normal from what I read it should be, no?

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The long term looks within spec. The short term suggest the engine computer is seeing a lean condition and having to correct by injecting more gas as you stop with the engine cold. Again indicating a possible air leak. Air leaks will show up more with a cold engine than a warm one. Warm engines don’t need nearly as much fuel for the same air flow compared to a cold engine.

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Hrmm… Thanks - I’ll look into that. That should also manifest itself as a non-steady vacuum pressure while idling, no?

11

Checking the intake manifold vacuum is a good place to start. It should be steady at idle, around 17-22 inches hg.