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Thread: TBI with High Idle in PARK

  1. #31
    Electronic Ignition!
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    Thank you Tayto
    Yes the truck is still setup with TBI...The TB is not the issue, I have tried a few different setups. This is a real head scratcher I've tried everything except wiring harness stuff. Remember if I jumper the ALDL and drive the IAC closed, then unplug it and start it up it will idle at 500-525... plug it back in and start the truck.... and back to 900 it goes. Something is telling the IAC to open and all I can think is wiring resistance, short or ground. My next step is to build a new pigtail and run the four wires straight from the IAC to the computer and see if that helps

  2. #32
    Super Moderator dave w's Avatar
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    The attached pics show the wiring differences between the IAC for a SBC and the IAC for a BBC. Circuits 441 and 442 wired differently, SBC vs. BBC

    Gearhead-efi link to the 1227747 wiring diagrams: http://www.gearhead-efi.com/Fuel-Inj...Information-42

    Seems unlikely the IAC wiring would be incorrect, but maybe?

    OTC might still offer an IAC tester: https://www.otctools.com/sites/default/files/103378.pdf

    dave w
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  3. #33
    Fuel Injected!
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    ohm out the wires and confirm pin locations. before running new/temp wires. my other thought was A/C request, if it is on it will bump up the idle.

  4. #34
    Electronic Ignition!
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    I double checked all this, the wiring is correct for a SBC. Thanks, Jason

  5. #35
    Electronic Ignition!
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    The wires are located correctly and seem to all Ohm correctly ….. I'm stumped

  6. #36
    Fuel Injected!
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    throttle cable holding throttle blades open?

  7. #37
    Electronic Ignition!
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    Quote Originally Posted by tayto View Post
    throttle cable holding throttle blades open?
    Thanks Tayto... but that was confirmed long ago! this is much deeper than something that simple.

  8. #38
    Fuel Injected!
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    Are you using the manual bin that dave w had posted and the problem still persist? By any chance are you running with a 180 degree T-stat? IAC logic doesn't play nice with colder than stock T-stat unless you change the parameters in the bin.

  9. #39
    Electronic Ignition!
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    Quote Originally Posted by stew86MCSS396 View Post
    Are you using the manual bin that dave w had posted and the problem still persist? By any chance are you running with a 180 degree T-stat? IAC logic doesn't play nice with colder than stock T-stat unless you change the parameters in the bin.
    Yes still running the manual bin and unfortunately the issue is still there. I'm not sure what Tsat in there but remember this issue has ran through several different computers, different engine and different programmers.....but same harness...

  10. #40
    Fuel Injected!
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    Idk which came first...the manual bin or the xdl. The xdl still reports the tune in park, then drive which the idle rpms seem normal but flares back up when back in park. Idk what ill effects i.e. cold starting, this might have since you're running an automatic but have you considered de-pinning the P/N switch? I just find it odd that its reacting to the P/N switch when you're using a manual bin???

  11. #41
    Carb and Points!
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    I have seen exhaust leaks do this before on TBI setups. I have held off posting because honestly the IAC value is throwing me off. but something to look for. usually near the O2 sensor.

    Btw this is my first post on this forum. i was an ASE master tech once apon a time. but joined the army in 2008 so ive been out of the pro game for a while. But i retired young so now i piddle a little. Current project is a 72 C50 Tbi swap.

  12. #42
    Fuel Injected! brian617's Avatar
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    To clear up some confusion and wild guesses what you are seeing in the data pids is Commanded IAC steps, not Actual IAC steps. So think about that for a minute and what youre seeing is what the PCM wants the IAC to be. That means something in the bin. or a related sensor feed back is telling the PCM to park the IAC at the value you see.
    89 K1500 Scottsdale 5.7L 5spd 3:42

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  13. #43
    Electronic Ignition!
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    Thanks everyone! I have no ability or skills to mess with the computer/tuning but aside from that I can handle the other stuff. In all fairness I have had three tuners attempt fixing this.... but to me it really seems like the computer is telling the truck to idle at 900 in park or some kind of wiring issue. I'm thinking about installing a new wiring harness...I don't know what else to try. Again thanks for everyone's help, we will get there! Jason

  14. #44
    Fuel Injected!
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    have you verified your p/n switch? unplug it and then look at wiring diagrams and emulate it being in park and neutral by adding or removing a jumper.

  15. #45
    Fuel Injected!
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    Quote Originally Posted by stew86MCSS396 View Post
    Are you using the manual bin that dave w had posted and the problem still persist? By any chance are you running with a 180 degree T-stat? IAC logic doesn't play nice with colder than stock T-stat unless you change the parameters in the bin.
    I'm gonna recant the T-stat comment as I've looked at some old logs of another '7747 project that I've worked on and temps stayed in the same range as your xdl if not cooler! Don't want you chasing ghost on my account.

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