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Odd idle only when cold, misfiring


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Let's start with "Don't worry!" ;)

 

Cold (As in wintertime) idle, but also slow cruising after a cold start is not the strongest point of all Subaru turbo-models.

 

The (self heating) Lambda sensor is having more difficulties warming itself up to it's working temperature in cold conditions.

It takes a lot longer compared with warm conditions.

 

During the time it is not yet on it's working temperature, your fuel-mixture is therefore pretty on the rich side, and your ECU can also not yet run a quick closed loop mixture. ( Aprox. 2 loops per second in warm conditions)

 

This will give two effect's:

 

-Very feelable 'closed loop' cause of wider mixture levels (lean-rich) and lower frequency. ('Elastic going up and down' feeling instead of smooth engine run)

 

-Misfires due to the very rich mixture peeks (In the closed loop) plus the fact the engine is still cold.

 

 

Once Lambda (And engine) is on working temp, it will run normally.

 

 

Hint: This can also occur when your Lambda has had it's best time, in warm conditions. You will then also notice it's using more fuel.

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Same issue this morning, guess Ava is having a rough couple of weeks. First started with the cruise control not working, followed by TCS and ABS light on with brake light full on, followed by a nail in my tires, followed by rough idle and p0171 this morning. "pulls hair out", did i mention this all happened since last wednesday?
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P0171 seems to indicate that you do have a vacuum leak, so go search with a spray and see what happens.

 

Cruise Control is automatically disabled as soon as there is a fault detected so don't worry too much about that. It's just a safety precaution.

 

As for the ABS/TCS - it may actually be related to the nail in your tires since the pressure fall can make the rotation "odd" and then the sensors gets an unexpected reading and throws an error.

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I don't want to deal with the hassle when I am capable of doing this fix, and the gaskets are only $20 total.

 

I just replaced the intake manifold gaskets (orange o-rings). The old one's looked to have some black leak spots but we won't know till I start it up tomorrow!

 

There have been a couple people reporting rough idles and misfires/lean with pinched/uneven o-ring gaskets when in cold weather, and resolved once the block warms.

 

http://lh5.ggpht.com/_32h1SNQWimc/TQb4Uxk3VuI/AAAAAAAAASE/xHXWQLpXwmc/s400/photo_1.JPG

 

http://lh5.ggpht.com/_32h1SNQWimc/TQb4g35_OcI/AAAAAAAAASI/2lEWgPHWX4E/s400/photo_2.JPG

 

 

might be tough to see but the black spots on the contact surface is bad. BTW the new o-rings have a squarelike edge, not rounded like the one's pictured. The new one's give more of a contacted surface from the gasket to the aluminum.

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Everytime I need to do something to my car I need to go to a friend's garage. I don't even have a driveway let alone an unheated garage!!! God bless my friend though, life saver.

 

 

I will be doing a boost leak test tonight as well as an intercooler reinstall.

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  • 2 weeks later...

Problem solved - intake gaskets. Tune / boost was fine - OP just used a crappy gauge ;)

 

Willy - lean code indicates a vacuum leak or pre turbo leak or problem. Your fuel trims left +/-2%. To hit 15+% to throw that code something has changed. You may have to pressure test the vehicle and check all pre turbo connections and the inlet. Problems like that don't come up 2 months after a tune :)

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The inlet hose clamps get loose as a goose in this cold weather if not tightened before, also the intercooler to intake manifold rubber pipe can also get super loose. Either way, I didn't have a boost leak, but I found those hoses to be "wiggle" loose.

 

 

I can say for certain though that those intake gaskets solved the misfiring in the cold

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  • 4 weeks later...

Crap... I was really hoping it wasnt something this deep. However I don't get and SES Lights I just have the rough idle ant some points and 15 vac reading.

 

Time to do some testing to see what I can find, but I just hope I don't have to pull the top end apart, but if I do I'm definately going to clean the TVG's while I'm in there.

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07-08 are the same and I believe that 05-06 are the same as well. I also have 110k on my car so it wouldn't surprise me either. It's just the fact that I just got my car running from over a week of part delays when I replaced my clutch, and the last thing I want to do is take it apart again.

 

Also sucks that no one in my area stocks those... I hate advance auto sometimes.

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FWIW, my issues with this problem have not occured since my recent upgrading to the lastes Cobb AP and a street tune last week.

 

The week before the engine stalled when I pushed in the clutch to slow for traffic on the highway. The night before the tune, after shuting it off on the driveway. I decided it was safer to drive to the mailbox in the snow storm then walk down. I went out started the car and seemed to run on 3 cylinders till I rev'ed it a couple of times.

 

I driven about 500 miles since the tune, no issues.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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FWIW, my issues with this problem have not occured since my recent upgrading to the lastes Cobb AP and a street tune last week.

 

The week before the engine stalled when I pushed in the clutch to slow for traffic on the highway. The night before the tune, after shuting it off on the driveway. I decided it was safer to drive to the mailbox in the snow storm then walk down. I went out started the car and seemed to run on 3 cylinders till I rev'ed it a couple of times.

 

I driven about 500 miles since the tune, no issues.

 

 

sounds like a different problem than mine. mine never stalled, but felt like it was going to. my idle has been raised to 750 anyway from my tune...that may have caused mine not to stall

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Got a damn SES light on my way home last night... Never happened before but now that I spoke of it I got it... Misfire on 1 2 3... so I pulled it into the garage last night, obviously the car was warmer than it was when I started, but I let it sit for about 2 hours and then I did a vac leak check using carb cleaner... Found nothing with that method... So I just put some seafoam in the gas and cleaned my maf sensor.

 

Didn't act up this AM but it wasn't nearly as cold, so we'll see how it goes for the next week or so.

 

I may order those gaskets to just do them and eliminate it as a possibility.

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Yes, happens when its very cold outside, or if my car spends the night in the driveway and not garage, which is typical. And it seems to get better as the car warms up, if not goes away completely. Only the day of REALLY cold temps did it continue longer than normal.
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