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About two weeks ago my WRX started stalling the engine when I would push in the clutch and shift to neutral as I came to a stop.  It seems like as the engine comes up to temperature, it looses its ability to keep the engine at idle.  Eventually I have to hold the throttle cracked open at idle to keep it running.  If I coast, in gear, up to a stop and disengage the clutch just as engine RPM reaches hot-idle, I can keep it running, no problem.  But if I come to a stop quickly and push in the clutch, the engine will immediately stall.  There is NO high idle, only a gradual reduction of idle speed as the engine warms up.  I haven't done much fiddling lately, besides replacing the MAF and front O2 sensors.  I'm also not getting ANY OBD fault codes.

 

Doing some research pointed to the IACV being gummed up.  So I cleaned it, per the instructions on NASIOC.


My drive to work involves about two miles of surface streets until I get to the freeway onramp, then about 8 miles of highway.  There are three stop signs between my house and the freeway and about as many between the freeway offramp and my work.  The car started pretty normal the next morning, but each time I stopped at a stop sign the idle would get lower and lower until the engine stalled as I pulled up to the stoplight at the onramp.  Same story after driving on the highway, when I pulled up to a stop after exiting, the engine stalled.

 

Some further reading of the IACV-cleaning post on NASIOC revealed that disassembly of the IACV could yield better cleaning results, but often the cleaned valve would fail within the next few months or years.  I decided to just bite the bullet and replace the IACV with a new one.  Same story.  The engine started fine, but with each stop sign between my house and the freeway onramp, the engine would idle lower and lower until it stalled at the onramp.

 

After the IACV, most folks suggest checking for vacuum leaks.  I haven't done this yet, but I'm very doubtful that there are any.  I haven't taken anything apart recently, save the new sensors, and the car was running perfectly normally up until two weeks ago.  I plan to do some data logging tomorrow on my way to and from work, and will post the results here.

 

So, anyone have any ideas?  Fuel pump?  Fuel pump relay?  Bueller?  Bueller?  Bueller?

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Check for a Vacuum leak. Broken/cracked hoses happen with age. Don't have to mess with them for them to split.

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Ahhh, I knew I was forgetting to mention something...  I replaced EVERY single hose at 90k miles (Currently @ 120k) when I replaced my shortblock, so I would be VERY surprised if anything was cracked or brittle at this point, but I will check that this afternoon.

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Was it doing it before you replaced the MAF? The dieing out could be an unmetered air leak anywhere between the MAF and the heads, or it could be a bad signal coming from the MAF. What's the code reader live data for MAF flow at idle? You could compare that to a known good car. If you replaced all the hoses, could one have not been clamped tight enough and it slipped partway off under boost?

 

I know gen1 EJ's would stall coming up to a quick stop if the clutch switch wasn't working, but gen 2's they changed the tuel cut coast to idle fueling strategy and eliminated the switch.

Edited by WoodsWagon

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+1 on the above.

 

Did you swap out the turbo inlet hose? - they get old and crack @ the turbo's inlet...and are PITA to replace w/out pulling the IM.

 

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Did you replace all the vacuum hoses with Subaru hoses? The parts store cheapo hoses don't last long. Have had a few of those break again after even just a few months.

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vacuum gauge might be helpful here.

 

does run OK when cold? maybe engine temp sensor is bad - choking a hot engine?

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The MAF and front o2 sensor were replaced as maintenance items.  Had been throwing an o2 code under sustained WOT, but those was replaced months ago.  I'll be doing some data logging on the way home from work today, so I'll have the MAF voltage data for review then.

 

Most of the hoses have either a worm gear clamp on them, or at least two zip ties.  The complex molded hoses were replaced with OEM rubber and the simpler ones were replaced with silicone.  The inlet hose has been replaced with a Perrin inlet, all connections zip tied or clamped.

 

The car runs really well when cold, and runs well when warm too, besides the low, hunting idle and stalling approaching a stop, when hot.

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Since I replaced the IAVC with a new part the engine doesn't stall as predictably as it used to, but the RPMs still drop to as low as 400 RPM at hot-idle.

 

I was finally able to capture the behavior in a log file (but will have to attach the link later, can't copy paste for some reason).

 

Are there any useful parameters that I left out?  As you can see, my engine speed plummets to zero after hitting the clutch as I slow for a stoplight.


I fiddled with the IACV connector and wiring harness this afternoon while the engine was running.  I also sprayed the inlet/IC/manifold with starting fluid.  Both tests proved inconclusive.

 

I have noticed on two occasions, since the idle issue emerged, that the car was difficult to start after it had been sitting for two to three hours.

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I have noticed on two occasions, since the idle issue emerged, that the car was difficult to start after it had been sitting for two to three hours.

 

This may point to a leaky fueil injector.

 

I'd also replace the CTS, if not already done...they can show/test 'good' but be borderline and cause issues.

Edited by wtdash

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I will look up the test for the CTS when I get home today.  My logs show pretty normal temps, but I'm not exactly staring at the readout as I drive down the road.

 

How would I check for a leaky injector?

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I have not had a chance to test the CTS yet, but it was suggested that my injectors might need cleaning.  Any thoughts on that as a root cause?

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live data may show what's happening as it warms-up.

 

you may need to find a way to log data - RomRaider or FreeSSM and laptop, maybe an app on a smartphone and an elm327 BT adapter?

 

look around here; http://www.subaruoutback.org/forums/65-parts-accessories-performance/39426-freessm-complete-access-your-ecm-tcu.html

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I have a Tactrix cable and RomRaider loaded on my laptop.  The problem is that I'm unable to copy/paste on USMB for some reason, which makes it tough to link to anything.

 

I will try linking to my log file on a different PC.

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Yes, brand new OEM IAC with a new OEM gasket.

Edited by carfreak85

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