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Extremly extremly high idle, wth??

This is a discussion on Extremly extremly high idle, wth?? within the General Help forums, part of the LSx Technical Help Section category; So im driving home tonight and my car randomly starts to take off on me while im in gear cruisin ...

  1. #1
    Member ldurham's Avatar
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    2000 Camaro Z28

    Extremly extremly high idle, wth??

    So im driving home tonight and my car randomly starts to take off on me while im in gear cruisin at 20 mph (its a m6) and i push in the clutch and the rpm's jump up to 3500 so im like wtf?? so i come to a complete stop and the idle stays at 3500 fluctuating +- 500, so i kill the engine and start it back up and its idling back to normal at 600 rpms, i start going through the gears not driving hard but get up to about 45 mph and it starts to take off on its own again so once again im like wtf?? i start coming to a stop again and it seems like the rpm's are wanting to drop a little as im slowing down and once i come to a complete stop its at like 2500 rpm and stays there for about 5 seconds and then drops down to 1k then 800 then 600, soo i take off again going through the gears, sure enough it starts pulling on its own so im frustrated now trying to figure out what could be causing this...doesnt seem like a vacuum leak since sometimes when i kill it and retart it it idles normal, but when i bought the car and got home with it i was changing air filters to an amsoil ea synthetic and noticed some one de screened my maf :/ so i starting thinking that was probably it but even if that was it and the maf was reading that more air was coming in than usual my throttle plate is still closed not allowing enough air in to idle at 3500 rpm.. and no ses light came on, im kinda stumped right now any advice from experiences like this is appreciated, also tonight was the first time ive driven my car in sub 50 degree weather, it was acting normal when the son was up at about 60 degrees but when the sun went down it dropped to 46 degrees and thats when it started acting goofy

    my mods are air lid, egr and air delete w/ tune out, lt's 3 inch true duals, ls6 cam, ls1 intake, dyno tuned by some place up north, and of course de-screened maf which i dont like and am scraping for monies to buy a new one
    Last edited by ldurham; 10-28-2011 at 09:37 PM.

  2. #2
    Member 383ls6's Avatar
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    red
    2002 z/28

    you may have a TPS problem. do you have access to a scan tool? or a DMM?

  3. #3
    Member ldurham's Avatar
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    Not until i get to work on monday, I was hoping this exact problem has happened to someone before and they knew which component is was that was bad so i didnt have to wait till monday to diagnose it

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    Senior Member Lunatikgixxer's Avatar
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    Bat mobile black
    2000 Trans am WS6 M6

    What kind of spark plugs are you running? My car did this when i had a broken spark plug tip broke off.... It would idle so high at like 4k after a pass.... I couldnt figure it out for the longest time then i took the spark plugs out one day and one was broken off -_- I changed it out and it fixed it instantly.. They were TR6's. Id check those if you havent recently..

  5. #5
    Member ldurham's Avatar
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    Tr 55's, I will check them wen I get home today, thanks for the advice, that's weird that a broken spark plug would do that I wonder why it would do that?

  6. #6
    Member ldurham's Avatar
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    And was it the porcelain part that was broken or the electrode part in the combustion chamber?

  7. #7
    Senior Member Lunatikgixxer's Avatar
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    Bat mobile black
    2000 Trans am WS6 M6

    electrode... the very tip of it in the chamber.

  8. #8
    Member ldurham's Avatar
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    Well I swapped the maf the iat and tps sensors with good known sensors and it didn't change a thing sooo I had it running and unplugged the idle air control valve and the idle sated exactly where it was at, soo when the idle dropped down to about 1,100 I unplugged it again and it stayed at 1,100 and never acted up again so I'm convinced that it is the iac, so I'm gunna get that part and throw it on, but I won't be able to drive my car again till I get all new tires they are dri rotted and cracked and are 7 years old and I blew one out on the highway today racing a Porsche lol

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    Senior Member Lunatikgixxer's Avatar
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    Bat mobile black
    2000 Trans am WS6 M6

    lmao nice job... well let us know if you get it fixed

  10. #10
    Smiles for 9.5 Years cammed goat's Avatar
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    I was going to suggest the IAC, but I see you corrected the issue. You DID clean the IAC and the port in the throttlebody where the IAC goes...right?

  11. #11
    Member ldurham's Avatar
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    Haven't corrected it yet cammed goat, the throttle body is clean as a whistle! But no I have not cleaned the iac pintle or the iac passage through the TB, I will be sure to do that before info buy a new part and see if that fixes it, especially since I have to buy a thousand dollars worth of tires lol

  12. #12
    Veteran 0rion's Avatar
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    vacuum leak or an air leak post MAF. First place to check is the pcv hose that goes into the side of the intake....check the back of that bend and see if it's cracked. Make sure your intake tract is sealed up. You can then start checking all other vacuum lines for leaks and around your intake for leaks. Either spray with carb cleaner or use propane which is safer although I've used carb cleaner numerous times and have never burst into flames. Good luck......

  13. #13
    Member ldurham's Avatar
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    Thanks for the info but I figured out it's my intake air control valve, I'm gunna try to clean it and if that don't fix it I'm getting a new one

  14. #14
    Member ldurham's Avatar
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    Well i put a new IAC on it and it did not solve my problem. I know its not a vacuum leak because i can kill the engine when it is idling high at like 3,000, disconnect the battery and start it back up and the idle drops down to normal.I dont know why the pcm is commanding the IAC in and out but im going to take it to work saturday and put the scanner on it and see if i can see anything out of the ordinary. Ive already swapped the IAT, MAF, TPS with known good parts and didnt change a thing. Only way i can get the idle to stay under 1000 rpm is to disconnect the battery then start it and then unplug the IAC.

  15. #15
    Smiles for 9.5 Years cammed goat's Avatar
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    Did you drive the car to set the IAC? 35-40 mph for 5 miles I believe.

  16. #16
    Member ldurham's Avatar
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    Quote Originally Posted by cammed goat View Post
    Did you drive the car to set the IAC? 35-40 mph for 5 miles I believe.
    No I did not do that I've never heard of that. All I did was put the new part on start it, it idled fine for 30 seconds then jumped to 2k, so I killed it disconnected the battery and reconnected it then started it again and it idled fine again so I backed it out the driveway and made it half way down the street before it started idling at 3k

  17. #17
    Member ldurham's Avatar
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    well i finally got it on a scanner today and everything looked normal. So i checked continuity on all the wires from the pcm to iac, low and behold the very last wire i checked was shorted, i traced it to the back of my right hand side valve cover. What a find. Oh and I looked up the relarn for the IAC for a m6, basically disconnect the battery reconnect it, make sure engine temp is above 179 i think, start and idle engine for 5 minutes the shut off for 30 seconds and thats it.
    Last edited by ldurham; 11-11-2011 at 08:09 PM.

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    Pewter
    1999 LS1 Transam

    ok guys looking for some help me and my turner are getting into it. And I cant find any answers anywhere! I jut did a motor build and he tuned my car before everything went fine I ended up having to replace the pcm and alternator. So he retuned it and it is idleing around 1800 to 2000 and it wont calm down. Any suggestions on what it could be?

  19. #19
    Spaz is My Mentor SMWS6TA's Avatar
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    Dave

    Have you checked for common culprits? (IAC, PCV vacuum leaks, TPS, MAF - has it been cleaned?, plugs/wires)

    Why was the pcm/alternator replaced?

    Does he (tuner) have the cam and head specs or current engine specs?


    Are you able to post a video of it idling?

  20. #20
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    I can get you the video later this evening maybe. It has new plugs and wires, the computer was replaced cause it put out 12.1 volts to the alternater which caused it to blow, thats why i got new ones, I checked the TPS its good, I havent cleaned the mass air flow though. what is the IAC? The motor specs are - Texas speed Cam 233/239 603 lift, it has dart pro 1 heads 225, ls6 intake,long tube headers slp 3/4 , magnaflow 3" inch no cats, ls7 lifters and 650 springs brand new head gasket, and header gasket. Circle d stall 3800 rearend Ten bolt 373 gears. Its weird like when it idles its at 1800-2000, but there is no lack of power if u put your foot in it. The sadest part is I havent put no more then 1000 miles on the car since the build and the stall and rearend i did a week ago havent drove more then 10 miles on em due to me being afraid of the high idle and it causing damage or etc

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