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Thread: Idle above 1500 RPM and won't settle.

  1. #1
    turbo addict
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    Idle above 1500 RPM and won't settle.

    1987 Shelby Z 2.2 one piece 555 stock exhaust manifold and turbo.

    Idle is consistently between 1600 and 1900 RPM

    Codes 12, 15

    I've checked for vacuum leaks, disconnected all vacuum lines except for MAP and Brake Booster lines. The code 15 is new, it didn't show up til today. I noticed that the O2 sensor was throwing first lean too long and then rich too long so I went ahead and installed the LC1 I had. No 02 codes right now but my scanner shows the 02 voltage is 1.02 and doesn't change.

    The code 15 is speed sensor and one of the triggers is the idle being more than 800 RPM higher. Is the SDS my problem or should I still look at maybe a leaky intake gasket? I've tested best I can for a leaky gasket but kinda over the problem at this point.

  2. #2
    boostaholic
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    Re: Idle above 1500 RPM and won't settle.

    I had crazy idle issues till I replaced the SDS. For the longest time i had no code till one day the speedo quit and then got code 15. Since new sds idle has been good...knock on wood.

    Here is one of the things i believe was due to the sds on its way out:

    http://youtu.be/q0z2-A0xCpg

  3. #3
    Supporting Member II Turbo Mopar Contributor ajakeski's Avatar
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    Re: Idle above 1500 RPM and won't settle.

    If you have access to a scanner, see if the SDS is reading any speed other than zero when not moving.
    that should give you an idea if it's good or not.
    Check the wires going to the SDS. Years of heat make them brittle. There could be a bad connection.

  4. #4
    Supporting Member Turbo Mopar Contributor GLHS60's Avatar
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    Re: Idle above 1500 RPM and won't settle.

    Also, any chance the base idle screw has been "adjusted" ??

    Thanks
    Randy


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    Randy Hicks
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  5. #5
    turbo addict
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    Re: Idle above 1500 RPM and won't settle.

    The idle screw still had the cap in it, I did attempt to adjust the idle with it but no dice. I'll have to set the base idle after I figure this issue out. I'll check the wires tomorrow, just thought it was weird I was getting O2 sensor codes then all of a sudden a few days after the issue starts I get the code 15. Now that I think of it the speedo doesn't work in the car, and I verified the sensor was plugged in so it's either a bad plug or bad sensor.

  6. #6
    See me ride out of the sunset... Turbo Mopar Staff BadAssPerformance's Avatar
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    Re: Idle above 1500 RPM and won't settle.

    As said, check SDS and wiring and also check the orange fusible links behind the battery. I had similar symptoms and code 15 and didn't figure it out until it didn't start and found a corroded wire next to a link which was still good but the wire was toast

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  7. #7
    turbo addict
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    Re: Idle above 1500 RPM and won't settle.

    Figured out the SDS plug on the harness was gone. Wired in a new plug and put in a good SDS. Reset the computer, fired it up, no codes, still idles at 2000 RPM. At this point I'm done with the car, its for sale. If anyone has any ideas feel free to chime in.

  8. #8
    boostaholic
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    Re: Idle above 1500 RPM and won't settle.

    I guess you have tried the base idle screw in the throttle body? I would almost be tempted to try a new throttle body.

  9. #9
    The moderately moderate moderator Turbo Mopar Staff
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    Re: Idle above 1500 RPM and won't settle.

    Also, George, clean the IAC port and throttle body before you set the minimum idle.
    Bryan
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  10. #10
    turbo addict
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    Re: Idle above 1500 RPM and won't settle.

    Swapped over a different TB with different IAC and TPS. Still did it. Drove it around the block and the car idles around 3k until I came to a complete stop and idles around 2k now. Unless it's a wiring harness fault or a bad computer I'm thinking it has to be the intake gasket.

  11. #11
    turbo addict
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    Re: Idle above 1500 RPM and won't settle.

    Did you plug the intake manifold support bolt hole?

  12. #12
    turbo addict
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    Re: Idle above 1500 RPM and won't settle.

    One piece intake.

  13. #13
    The moderately moderate moderator Turbo Mopar Staff
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    Re: Idle above 1500 RPM and won't settle.

    Have you tried spaying carb cleaner around all the gasket mating surfaces, connections or plugs to see if the idle changes?
    Bryan
    86 GLHS #161, 2016 Impala
    SDAC National Member, SDAC Buckeye Chapter Member

    A man has got to know his limitations.....

  14. #14
    turbo addict
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    Re: Idle above 1500 RPM and won't settle.

    Yeah, I sprayed the top of the intake. I've pulled the tb off twice ams the last time I put on a new one.

  15. #15
    turbo addict
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    Re: Idle above 1500 RPM and won't settle.

    Completely block off throttle body and see what it does. It will drop to a normal idle if its a vac leak it will stall if its a throttle body or computer issue. It it drops to a normal idle you can then check for vac leaks easier because the engine is quieter.
    Ian Adams Function>Form 1990 shadow scrapped, too rusty:( 1991 Spirit R/T Scrapped, parts sold:( 1989 Turbo Caravan Daily beater with built-[I]ish [/I]​engine slowly evolving into weekend turbo beater.

  16. #16
    Hybrid booster
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    Re: Idle above 1500 RPM and won't settle.

    Brake booster leaking? With the car off, you shoud have 2-3 assisted pumps before the pedal gets hard. If it gets hard right away, you have a leak. I myself would try and reset base idle first following all the steps, before trying to chase vaccuum leaks.

  17. #17
    turbo addict
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    Re: Idle above 1500 RPM and won't settle.

    Quote Originally Posted by shackwrrr View Post
    Completely block off throttle body and see what it does. It will drop to a normal idle if its a vac leak it will stall if its a throttle body or computer issue. It it drops to a normal idle you can then check for vac leaks easier because the engine is quieter.
    I'm going to try this next.

    - - - Updated - - -

    Quote Originally Posted by turismolover22 View Post
    Brake booster leaking? With the car off, you shoud have 2-3 assisted pumps before the pedal gets hard. If it gets hard right away, you have a leak. I myself would try and reset base idle first following all the steps, before trying to chase vaccuum leaks.
    I've blocked off the booster vac hose and no change. I'm 99% sure there is not a vacuum leak unless its the map sensor itself or the intake gasket. All the vacuum ports were blocked off except for one on the intake that the MAP was hooked to.

  18. #18
    Hybrid booster
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    Re: Idle above 1500 RPM and won't settle.

    I sometimes have this issue with the Omni. I can drive around fine but some times when I am coming to a stop, the idle will stick around 2500 until I come to a complete stop, then the engine settles down. I had the same issue with a Shelby Charger, T1, but it was bass ackwards. Start it up and the idle would shoot to 3000 until you started moving. Then it would be happy, until you came to a dead stop, then it shot way up again. Talk about frustrating..

    Anyways, have you thought about the coolant sensor? I've read that engine computers take readings from the coolant sensor or intake air temperature sensor, or both, in order to adjust the idle. They do this in order to get the engine warm or to get it up to operating temps. Maybe try cleaning them?

  19. #19
    boostaholic
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    Re: Idle above 1500 RPM and won't settle.

    All my idle issues were solved with a nos speed sensor.

  20. #20
    turbo addict
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    Re: Idle above 1500 RPM and won't settle.

    If you have a scanner available, reading the idle control motor counts will tell you if the idle is a leak or commanded. 0 steps means a huge leak.

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