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Thread: bad idle

  1. #1

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    bad idle

    My truck is starting to not idle. If I put it in neutral at a light and hold it at 1500 it will be fine. If I leave it in gear it misfires and then sputters as I take off. It has to Rev up to clean out.
    It reminds me of my old drag car loading up and runs better after snapping the throttle to clean it out.

    I have no idea how a fuel injected engine would do that. The idle sometimes cycle up snd down too.

    It only seems to happen in closed loop.

    Amy ideas?

  2. #2


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    When was your last full tuneup?

  3. #3

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    its all new

  4. #4

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    sounds like bad spark, my 88 was doing similar and I just changed the plugs (today actually) the old ones were looking pretty old/fouled

  5. #5


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    Did you do all of it or did you just replace only a few things?

  6. #6



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    Have you looked for vacuum leeks? The hoses are nearly 30 years old so they do come apart. Also check for stretched timing belt. If you have never changed it. Do it now before you get stranded along the road.
    Members come and members go, But the board keeps track of them.
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  7. #7

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    Wires. .cap ..rotor..new timing belt...plugs

    I'm changing the fuel filter tonight. .

  8. #8


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    The only other probable issue (other than fuel filter) is the TPS. If it's worn out, or out of adjustment, it will act like that. A fuel filter will definitely do what you are describing if it is clogged though.

  9. #9

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    Ok...I have checked the tps and it is within spec..I was thinking egr too but haven't checked it.

    Now today it drove great...and I have done nothing to it

  10. #10

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    Well I swear the filter must have been original and some of the fuel that came out of the filter looked kinda brown at first.
    The truck got pep now and actually pulls past 4000 now

  11. #11

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    Look at the Idle air control valve (IAC) on the throttle body. this is most likely your problem if not part of it. The coils in the stepper motor go out and give you bad idle and eventual burn up your ECU, been there. Is the IAC brown or black?

    fallow this video on how to test the IAC:
    https://youtu.be/KibYz21IMA0
    It is the same testing procedure for all Mitsubishis up until about 2000.

    This is where you can buy a new quality IAC motor that is improved and reliable on the cheap:
    http://www.ninjaperformance.com/mits...8e12c33664589c

  12. #12

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    Please let me know if this works for you.

  13. #13

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    I will check this out next!!!

  14. #14

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    It started misfiring in gear at stop.lights again today.

  15. #15

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    The idle is cycling up and down...I think your right..The idle control.
    It's the black one.

  16. #16



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    it can also be the ECM - bad caps can cause this.
    Pennyman1
    The best Dodge that Dodge never made
    Living the D-50 lifestyle since 1980

  17. #17

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    http://www.ebay.com/bhp/mitsubishi-l...-control-valve

    Are they all the same?

    I can't find the part number to cross over to another brand.

  18. #18


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    They're not all the same.

    The jumpy/bouncy idle is usually caused by the TPS not responding correctly, or the ECU not knowing when the throttle is closed.

  19. #19

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    I can't get an IAC in canada for this truck.

    If I hop over the border to Autozone would anyone have a part number?

    The O'rielly's website give me a throttle speed valve not the IAC when I go on their site.

    I have found a few numbers but not sure. Any suggestions

  20. #20

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    I now see that the whole thing is a unit md614351....
    It has 2 plugs were all the replacements I've found have only one and the plugs don't match at all.

    I'm at a loss of what you could get at auto zone that could have replaced this....

  21. #21


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    I found this for a 1900 Ram50 http://www.rockauto.com/catalog/more...nid=600&jpid=6 its a 2 plug and you should be able to get it ordered from Canadian tire. I would order it from Rockauto as it will be 1/3rd the price even with exchange and shipping.

  22. #22

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    Holy crap...with exchange that's about $500 can.

  23. #23



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    Wouldn't be better to take the ECM out and check it for burnt caps or bad solder points before you spend all that money and it isn't the problem. It sure could be the problem and they are also easy to pull out, but if it isn't and you spend that cash, you will be kicking yourself even harder when your wallet is empty. Perhaps even try one from another truck if available before pouring out that kind of money.

  24. #24

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    Good idea..
    I have noticed that idle has improved since the fuel filter change and 4 containers of fuel injector cleaner run through the tank.

    The idle seems much less iratic.

    The tps and the motor sensor and servo checked in spec last night with the multimeter so I'm headed to the ecu

  25. #25

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    I am glad you fallowed the video I linked above and checked the coils on the IAC and did not just replace it.

    If you need a ECU rebuild send it to AV Pro, they do work for aerospace and have an excellent reputation along with a life time warranty for $190.00, or take your chances on eBay...

    http://www.avproecm.com/

    http://www.avproecm.com/mitsubishi.htm

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