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PostPosted: Wed Jul 31, 2013 8:45 am 
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Location: West Des Moines
I have a 1990 GMC truck with a 5.7 liter V8. The engine has been rebuilt, prior to me purchasing it, and has a new cam and heads. The truck runs fine at speed but it idles too low, roughly 400-500 in gear. It appears the idle is controlled by the computer. I have been told by some mechanics and friends that I need to have the chip re-flashed, but they don't do that kind of work themselves. The truck is equipped with a throttle body injection.

Does anyone here know anyone or any shop that does re-flashing? I know Bob Brown does, but their guess it would cost me at least $500 to have it done there as they need to diagnose what is causing the low idle before they can raise it, etc, etc.

The truck does stall often when I put it into gear.

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PostPosted: Thu Aug 01, 2013 2:17 pm 
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Location: Oskaloosa
Could also just be a vacuum leak. I would check that first, since it would be a lot cheaper, and even if you do get it reflashed, and there is a leak, it still won't idle right.

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PostPosted: Thu Aug 01, 2013 10:45 pm 
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It is not a vacuum leak, or the computer, idle control unit, throttle positioning sensor, egr problem or anything of the sort. Everything is operating correctly. I simply have a low idle and re-flashing the chip appears to be the only solution, unless I switch to a carburetor.

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PostPosted: Tue Aug 06, 2013 8:32 am 
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You might check out getting a piggyback performance chip like what I have on the firebird! Motorvation makes them. They also do custom chips.

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    PostPosted: Wed Aug 07, 2013 8:14 pm 
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    Thank you for the info. I checked out their website but I did not find anything on a piggyback chip. I did find out that they make chips for my truck but I don't have the needed information so they can program the chip. I have no information on what cam is in the truck.

    From what I have learned I need to have a computer plugged into my computer and then using a program fine tune the variables on the engine to what is desired and then have a chip programmed.

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    PostPosted: Fri Aug 09, 2013 10:36 am 
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    Megasquirt.

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    PostPosted: Fri Aug 09, 2013 12:36 pm 
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    Thank you for you one word reply but from I read on their website not what I need. I am trying to find someplace locally that is cheaper than a dealership or an individual locally that knows how to reprogram my chip.

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    PostPosted: Fri Aug 09, 2013 1:12 pm 
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    Relax man, just having some fun. (and fwiw, MS would probably be cheaper than going to a dealer, and would solve your problem)

    I also found this.

    http://kevin108.com/?p=380

    And this

    http://www.ehow.com/how_7959677_reset-baseline-idle-gm-tbi.html

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    PostPosted: Fri Aug 09, 2013 2:31 pm 
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    Thank you for the info, but my throttle body unit does not have an adjustment screw. Some did and some didn't.

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    PostPosted: Mon Aug 12, 2013 10:36 am 
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    Jim, maybe give these guys a call? http://www.tbichips.com/

    I know a few folks with motorhomes who have used them with good results.

    Jarrod


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    PostPosted: Mon Aug 12, 2013 12:36 pm 
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    Thank you, but I CAN'T just order a chip. I do not have specs for the modifications done to my engine by the previous owners.

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    PostPosted: Mon Aug 12, 2013 1:48 pm 
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    Based on what you don't know about what the previous owner did, $250 and a trip to a dyno that can log the ACTUAL timing in conjunction with air fuel ratios would be good money spent, in my opinion. (Manual measuring/logging of the timing while on a load cell dyno that can hold the RPMs at set points wouldn't be out of the question, in my mind.)

    Is the assumption that the chip in the ECU is currently stock, or is that in question as well? If you "know" it's stock, I'd guess the TBI folks (or others) should be able to raise the idle on a "stock" chip....but that also seems like it would be leaving a lot on the table with regard to the timing table built into the chip, knowing that it's got something else going on for heads and cam.

    As for local sources....

    Karl Performance? They've got a dyno, and I'd think with the 'Vette stuff they do they'd be able to log / analyze / reflash TBI chips? Likely guaranteed not to be the "low cost" solution.....

    Nostalgic Enterprises in Valley Junction? Maybe they've run into similar issues with their work on mid-80s TBI-based Vettes?


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    PostPosted: Mon Aug 12, 2013 3:10 pm 
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    I will pass on the information you provided to my friends who know more about this than I do. Thank you. It does have the factory computer and chip, and a OBD 1 port.

    fyi, Corvettes went from a carb, to Cross Fire injection (similar but not the same to TBI), and then to Tuned Port Injection.

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    PostPosted: Tue Aug 13, 2013 2:32 pm 
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    Jim Kirk wrote:
    I will pass on the information you provided to my friends who know more about this than I do. Thank you. It does have the factory computer and chip, and a OBD 1 port.

    fyi, Corvettes went from a carb, to Cross Fire injection (similar but not the same to TBI), and then to Tuned Port Injection.


    Wasn't sure on the 'Vette stuff - a quick Google search showed some folks talking about going to TBI, but now that you mention it I also remember hearing (from other sources) semi-awful stuff about Cross Fire....perhaps the TBI retrofit is a "solution" to handling Cross Fire? *shrug*

    In any case, good luck with the truck and if the folks you're chatting with want to know more about what I'm thinking (which might be dangerous), feel free....

    Jarrod


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    PostPosted: Sat Aug 17, 2013 10:19 pm 
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    Thank you all, went a different route on a solution. I used to have a tbi unit without a idle control screw so I got one that did. It is now installed and the idle has been adjusted. I still have an occasional minor fluctuation in the idle. I am declaring victory and moving on. Now I can add air conditioning to my truck, next year or the following.

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