2011 WRX with lumpy idle (cold engine)
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This is a discussion on 2011 WRX with lumpy idle (cold engine) within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; This just started two days ago. I start the engine and it has a very lumpy idle when cold. Ambient ...

  1. #1
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    2011 WRX with lumpy idle (cold engine)

    This just started two days ago. I start the engine and it has a very lumpy idle when cold. Ambient temp is not a contributing factor as it does it in the cool morning or hot afternoon. The car has 12k & no mods other than a crank pulley and pitch stop. After a couple of minutes when the engine is warm it idles fine. Noting one other thing it has always done that has been a concern is when coming to a stop and depressing the clutch pedal the RPM's drop almost to a stalling point then it recovers?

    I will be taking it to the dealer for diagnosis and repair, just wondering if anyone else has experienced this issue and what might be the cause?

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    Not sure about the lumpy Idle when cold, but I noticed RPM drop on my 2008 WRX and brought to a dealer and they said that it is normal and they all do this, however it isn't as noticable on my 2012 WRX.

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    Gold Member lokey's Avatar
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    I would be willing to bet that the reduction in load from the lw crank pulley is causing both of your issues. Which one are you using?
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    The Cobb pulley. It has been in place for about 7 months with no issues.

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    Moderator T0rque's Avatar
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    When did you put in the pitch stop?


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    It has been two weeks since installing the pitch stop.

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    Pro Manscaper Mikie13's Avatar
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    why was the pulley one of the first and only things you've done?

    I've read where lightened pulleys can cause some roughness in idle.
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    Main reason I did the pulley was due too the time it took the rpm's to drop between shifts.

  10. #9
    Pro Manscaper Mikie13's Avatar
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    Interesting. Has it made a difference?
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  11. #10
    Registered User maus's Avatar
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    My guess it the pulley, I have seen on other cars lightweight pulleys causing idle issues.
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    I would guess pulley also. But it has not done it since yesterday with 4 cold starts since. I am going to look for a loose vacuum hose or something else loose. I am going to clean the MAF also. I would think if it were the pulley it would have manifested itself long before and be at every idle. Since it only happens when the engine has sat for at least 8 hours it may have something to do with cold engine emissions?

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    Quote Originally Posted by Mikie13 View Post
    Interesting. Has it made a difference?
    No power increase, the engine is just able to rev up & down quicker.

  14. #13
    Moderator T0rque's Avatar
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    I would guess you notice it now because of the pitch stop.


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    The pitch stop is like night and day... That and the Cobb shifter bushing is money well spent!

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    Started cold engine this morning and fine, nothing loose or leaking. Oh well then, if it does it again I will video it and take it to the dealership for them to figure out.

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