How to fix your idle surge problem.

Posted by 98autogstspyder, Jul 16, 2005
Articles: Engine & Fuel -

  1. 98autogstspyder

    98autogstspyder Awaiting Email Verification

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    92 Talon Tsi AWD, Florida
    In hopes to eliminate many of the posts in regards to an idle issue or "idle surge" I have put togethor a list of things to check when dealing with an idle problem. I would say that 99% of you will find the answer to your problem here. I have done a lot of research on this issue and if any of you have a question, feel free to PM me. Also if there is something you would like to add to the list let me know. Enjoy and good luck with solving your idle problem!

    Problem: Idle Surge

    Suspects:
    - Vacum Leak
    Check both gaskets on throttle body
    Check vacum line for break booster
    Check for any fault that is allowing air past the throttle plate
    For anything not mentioned here, doing a boost leak test is a good idea. Once all boost
    leaks are eliminated then continue.
    - Dirty Throttle Body- Dirt can cause the throttle plate to not close completely.
    - Replace the Fast Idle Air Valve (FIAV)- Costs about $140 new.
    - Check the cruise control cable- make sure it is not too tight
    - Check... the BISS, BISS o-ring, fuel pressure solenoid hoses, BOV return hose, egr seal;
    - Unplug... the Idle Surge Controller (ISC), adjust the BISS and reset the ECU
    the ISC is a stepper motor, it does not provide any feedback to the ECU, so the
    computer assumes it is working correctly. The ECU will never confirm a
    malfunctioning ISC with a ''check engine light'' code.
    - A bad exhaust leak can cause this. The mechanic I bought the car from
    told me that by me fixing the exhaust leak on my car, it would fix my problem.
    I dont fully understand why me fixing this would solve the problem.
    - Bad O2 Sensor
    - Bad Coolant Sensor
    - Bad Throttle position sensor (TPS)-Now I have read that the TPS is the culprit when the idle surge starts right after you start the car.
    - Bad ISC motor- Costs about $220 brand new. I have read that this is the culprit when the car starts to surge after it has been running for a while.
    - Bad throttle body seals- There are two seals in the throttle body that get old and need to be replaced after time. The fix is cheap, but digging into throttle bodies isnt the easiest of things.
    - Bad ECU- Not likely but remember the ECU is the brain of the car. There is a possibility that this can be causing your issue.

    With many of the parts I have listed here, I suggest getting togethor with a friend that has the same model has your car and start swapping out parts that you think might be bad. Read up and find out which parts are interchangeable between years. Also trips to a junkyard are recommended too. Many of the sensors and parts of the throttle body as well as the ecu are simply unaffordable if purchased brand new.


    I have gathered my info from various threads on this site vfaq.com and from experience.
    Here is another area that goes into more depth of what I am speaking of here: http://www.dsm.org/how-tos/tttt/tttt3.html It is also found in the Frequently Asked Questions area on this site.


    -Tyler VanDonge


    PS
    Here is a picture of the FIAV, because many people are unfamiliar with this. This photograph explains what needs to be done to your FIAV if you decide to block off your coolant lines running to your throttle body. If you do not do this, it can cause idle surge as well.
     

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