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Thread: Erratic RPMs at idle/start-up | Solved with fuel system cleaner

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    Erratic RPMs at idle/start-up | Solved with fuel system cleaner

    I have a 2015 Mitsubishi Mirage ES with a CVT, 128,412 miles. I’ve noticed recently that when I start up my vehicle that the RPMs will throb/surge from 800 to 1200 or so until the vehicle is fully warmed up, driven, etc. It doesn’t happen all the time, it’s more of a hit or miss. My thoughts are that it’s either the battery, which is aging, something with the fuel system, or perhaps the car converter. Anyone have similar issues?



    Forum member grevster had a similar problem that was solved with some fuel system cleaner. It's important to note that this is not a fuel treatment, but a cleaner such as Techron or as grevster used, Gumout:

    Quote Originally Posted by grevster View Post
    Here is an update, I used a bottle of Gumout all in one cleaner in a full tank of 87 octane gasoline (sorry, i could not find any techron locally) and drove 2 hours continously on the highway around 110 - 120km/h. The next morning, when i started from cold, i still had the erratic idle but this time it was not bouncing between 1100 rpm - 750 rpm but it was bouncing around 900 - 750 rpm. So the amplitude of idling bounce reduced.

    I gave another bottle of Gumout this time in half tank Shell 91 octane gasoline. It is still in the tank not finished yet but when i checked this morning, i didn't see any bouncing at all. Of course i need to check couple more morning cold starts to make sure but i guess it is getting much better and cleaner really helped. Thank you all!
    If you are having a similar problem and have tried a fuel system cleaner, please post your results.


    Last edited by Eggman; 08-29-2019 at 08:56 AM.

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    Quote Originally Posted by MrAmerica1776 View Post
    ...2015 Mitsubishi Mirage ES...128,412 miles
    ...RPMs will throb/surge from 800 to 1200 or so until the vehicle is fully warmed up
    ...doesn’t happen all the time
    Erratic idle issues in a drive-by-wire car (which is what the Mirage is) may be associated with a dirty/sticking throttle body. Pick up a $2 can of throttle body cleaner and take a shot at cleaning in/around the throttle plate.

    This post has pics of the throttle body:

    https://mirageforum.com/forum/showth...ll=1#post65169

    This thread talks about cleaning it...

    https://mirageforum.com/forum/showth...-Body-Cleaning

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 51.6 mpg (US) ... 21.9 km/L ... 4.6 L/100 km ... 62.0 mpg (Imp)


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    My '15 ES manual suddenly started doing that for a little while at somewhere over 100,000 miles...and then just as suddenly stopped doing it. If you are not getting any check engine light I wouldn't worry too much about it.

    Probably the idle air control valve getting a little sticky. Hondas are infamous for this. Couldn't hurt to run some fuel system cleaner through it. Techron or the like.

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    Quote Originally Posted by Cobrajet View Post
    Probably the idle air control valve getting a little sticky.
    That's what I was going to say, too. Then I found an old post from Doax mentioning that our cars don't have a dedicated IAC since they are drive by wire. I forgot about that.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 51.6 mpg (US) ... 21.9 km/L ... 4.6 L/100 km ... 62.0 mpg (Imp)


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    Quote Originally Posted by Top_Fuel View Post
    That's what I was going to say, too. Then I found an old post from Doax mentioning that our cars don't have a dedicated IAC since they are drive by wire. I forgot about that.
    Good call.

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    Quote Originally Posted by MrAmerica1776 View Post
    I have a 2015 Mitsubishi Mirage ES with a CVT, 128,412 miles. IÂ’ve noticed recently that when I start up my vehicle that the RPMs will throb/surge from 800 to 1200 or so until the vehicle is fully warmed up, driven, etc. It doesnÂ’t happen all the time, itÂ’s more of a hit or miss. My thoughts are that itÂ’s either the battery, which is aging, something with the fuel system, or perhaps the car converter. Anyone have similar issues?
    Steve doesn't have a CVT Mirage, but his car has almost twice as many miles as your car. He's been adding Techron to his fuel every time he does a tire rotation. A few issues he was sensing suddenly disappeared for him. It may be worth a try, & it surely wouldn't hurt anything (other than making your wallet a little lighter). It's what I would try first at least.

    This is one of Steve's recent posts -

    252,849 miles

    Getting the tires rotated and about to do another Techron treatment.


    I also heard recently a rough idle after a cold start may be cause by your fuel injectors being dirty. When cold, more fuel is required. Once the car warms up, less fuel is needed and the problem seems to go away. A bottle of Techron may address this issue, too. I haven't had the need to use the stuff, but I would try it in your case. Just a suggestion!
    Last edited by Mark; 06-13-2019 at 10:58 PM.

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    I started having the same erratic idling after the engine started from cold. I asked the local Mitsubishi dealership and although the car has still warranty on it, they suggested me having spark plugs replaced, throttle body cleaned and a treatment, totaling around $550.



    Solved:
    Quote Originally Posted by grevster View Post
    Here is an update, I used a bottle of Gumout all in one cleaner in a full tank of 87 octane gasoline (sorry, i could not find any techron locally) and drove 2 hours continously on the highway around 110 - 120km/h. The next morning, when i started from cold, i still had the erratic idle but this time it was not bouncing between 1100 rpm - 750 rpm but it was bouncing around 900 - 750 rpm. So the amplitude of idling bounce reduced.

    I gave another bottle of Gumout this time in half tank Shell 91 octane gasoline. It is still in the tank not finished yet but when i checked this morning, i didn't see any bouncing at all. Of course i need to check couple more morning cold starts to make sure but i guess it is getting much better and cleaner really helped. Thank you all!
    Last edited by Eggman; 08-29-2019 at 08:53 AM. Reason: Added solution

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    I took a car to the dealer that needed a new cvt. They suggested the same work be done. Car had 130k kms. Spark plugs don't need to be changed til 160k according to the manual. All the one's I've changed so far looked and worked fine still. Where in Alberta are you? Avoid south side Mitsu in Edmonton if you can. I'm constantly fixing stuff they can't diagnose that they won't cover under warranty.
    Truck
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    Optima

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    Quote Originally Posted by grevster View Post
    I started having the same erratic idling after the engine started from cold. I asked the local Mitsubishi dealership and although the car has still warranty on it, they suggested me having spark plugs replaced, throttle body cleaned and a treatment, totaling around $550.
    Make sure your oil filler cap is secure. I noticed erratic idle speed when loosening mine. Have you noticed any signs of leaks?

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.9 mpg (US) ... 21.2 km/L ... 4.7 L/100 km ... 59.9 mpg (Imp)


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    Quote Originally Posted by Fummins View Post
    I took a car to the dealer that needed a new cvt. They suggested the same work be done. Car had 130k kms. Spark plugs don't need to be changed til 160k according to the manual. All the one's I've changed so far looked and worked fine still. Where in Alberta are you? Avoid south side Mitsu in Edmonton if you can. I'm constantly fixing stuff they can't diagnose that they won't cover under warranty.
    I am in Calgary and there is a dealership in NE here. It has 120k kms on it. Did the cvt fail prematurely? 130k kms should not be much regarding their life span, i am scared!

    @Eggman, the oil cap was tight but i will leave a cardboard underneath to check for leaks overnight.



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