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Low Idle

Posted by BLACK'98DSM, Aug 19, 2019

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  1. BLACK'98DSM

    BLACK'98DSM Proven Member

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    I'm thinking it's because I need a tune, but let's hear your input.

    - Car idles at 750-850 rpms once warm.
    - Idle is a little rough (not bad, but noticeable)

    It's cammed, but only a mild exhaust cam shouldn't effect it this much, right?
     

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  2. techboy

    techboy Proven Member

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    There's a difference between a rough idle and a low idle. Your idle rpm is the recommended idle speed from Mitsu, so I don't think its low.

    Was it rough before you installed the cam? I'd bet the slight roughness you feel is related to the can or a slight vacuum leak. That's about the only other thing that would cause a rough idle.
     

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  3. BLACK'98DSM

    BLACK'98DSM Proven Member

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    I thought the rpm would be raised due to a vacuum leak?
    No, but it had a high idle so I can't vouch for how it would have been.
     

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  4. techboy

    techboy Proven Member

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    Often a vacuum leak will make it high, but I've also seen a rough idle in a DSM due to vacuum leak as the car tries to compensate for it. Now that you said it was high before the cam it makes me wonder even more. Often times it's the TB gasket.
     

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    1999 Mitsubishi Eclipse GST
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  5. 95_gsx_2g

    95_gsx_2g Supporting VIP

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    Just out of curiosity do you got any tuning software or is it just on a stock ecu? Aftermarket cams like my gsc 274s like to lope alot and sound alot more choppy compared to the stock cams which I absolutely love! I actually prefer a target idle of 950-1000ish idle in my dsm. It just drives better that way with all the mods and being a manual. Check good for boost leaks, bad isc, biss etc.
     

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  6. ThunderChild

    ThunderChild Supporting VIP

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    OP has a 420a just to be clear. I agree it sounds like it may be a vacuum leak. If the leak is small enough the car will try to compensate and it may cause a rough idle, especially with cams.

    What cam(s) do you have?

    Have you verified you don't have a fuel/spark problem?
    And have you verified mechanical timing is in spec?

    A video of the rough idle may help as well, could all just be a result of the cam lope.
     

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  7. BLACK'98DSM

    BLACK'98DSM Proven Member

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    The idle can be felt but not really seen. I thought since I only upgraded the exhaust cam it wounldnt have the typical cammed rumble effect. But maybe I was wrong.
    233 exhaust and stock replacement intake. They both came in a kit from carid.com a while back.
    For now I'm on stock ecu. I really badly want a Megasquirt, that is somewhere down the list of future mods.
     

    Road Race Build 2K  15

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  8. BLACK'98DSM

    BLACK'98DSM Proven Member

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    Good. Whatever then:D
     

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    1998 Mitsubishi Eclipse N/T
    fwd · manual · 2G DSM

    293  3

    2012 Murray Explorer Dune
    rwd · automatic · Misc Vehicles

    207  6

    2009 Troy Bilt Bronco
    rwd · automatic · Misc Vehicles
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