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Thread: Protege5 rough idle

  1. #1
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    Mazda, Protege5

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    Protege5 rough idle

    Hello everyone. I can't seem to find out the cause of my rough idle. I did use the search function however I can't seem to fix my issue.


    My 03' Protege5 has about 130,000 miles and I have changed/cleaned the following to try to fix my bad idle..

    *Spark Plugs
    *Coils
    *Coil wires/Plugs
    *Battery
    *Battery Terminals
    *Cleaned EGR
    *Reset ECU
    *Fuel Injector Cleaner
    *Cleaned MAF

    The car when cold will start up and have high revs and will drop down to about 200-300 rpm and then shoot up to 1k-700 RPM

    Thank you for the help. Sorry for Garbage formatting.
    Last edited by DayMan; 08-22-2017 at 07:02 PM.

  2. #2
    2008.5 MGM MS3 rsvinylgraphics's Avatar
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    Don't see cleaned MAFS on your list, maybe try that.

  3. #3
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    Sorry I did clean the MAF. No luck

  4. #4
    The Diagram Dude pcb's Avatar

    2002 mazda protege 5

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    Clean your IAC valve...
    Seafoam in your gas and up the brake booster vacuum line...
    The Diagram Dude

  5. #5
    The Diagram Dude pcb's Avatar

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    If you reset your ECU, it needs to relearn how to idle the car... Takes about 100 miles with lots of idling at different temperatures and other conditions...
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  6. #6
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    Thanks ill go do that and get back to you and see how it does! Thanks again!

  7. #7
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    Question. How do I "up the brake booster"

  8. #8
    Certified Mazda Tech hornsfan10609's Avatar

    2003.5 Mazdaspeed Protege x2

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    He means putting seafoam into the motor through the vacuum line for the intake manifold. This should not be necessary to resolve your erratic idle. Are there any CELs? I would suspect incorrect plug gap, dirty IAC or failing MAF sensor.
    Mod List. "Jinba Ittai"

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    2002 Red Protege5 RIP:4/25/10

  9. #9
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    Brand new maf. No CEL. Plugs I gapped correctly. IAC I cleaned. It seems to be better but not 100%

  10. #10
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    02 Mazda Protege5

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    I am having the exact same issue DayMan. Did you ever get it figured out? I swapped MAF sensors, installed new plugs, wires and IAC valve. I would like to know more about the idle relearn steps if anyone could help me with that, please help. My car has a manual trans also. What is the correct gap measurement on the plugs hornsfan10609?
    Last edited by Myers; 05-06-2018 at 03:10 AM.

  11. #11
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    Also how do I reset the ECU? These may be simple questions but I have limited automotive experience.

  12. #12
    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by Myers View Post
    Also how do I reset the ECU? ...
    Disconnect the negative battery cable, wait ten minutes, then reconnect it.
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  13. #13
    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by Myers View Post
    ... I would like to know more about the idle relearn steps if anyone could help me with that, please help...
    You just kinda wait for the car to do it's thing.
    However, if you give it lots of chances to bring your car to idle, it will happen faster.
    You could keep hitting the clutch and let it idle while you're coasting.

    My car almost stalls while it's relearning, some cars do stall. Keep that in mind while you're driving.


    Quote Originally Posted by Myers View Post
    ... What is the correct gap measurement on the plug?
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  14. #14
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    Thanks PCB, I definitely try these out.

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