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Thread: TBI 350 Target Idle Speed

  1. #121
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    You can test your ECU but it would require you to adjust your manual idle control.

    If you jump A & B or otherwise plug the IAC and adjust your manual screw to idle at about 600 rpm, the computer can't do anything about that.
    If, when you hook the IAC back up or unblock it, it jumps to 1000 rpm again, you should see the IAC open farther and the computer would be commanding that. If it stays at 600 rpm, your throttle plates are open too far and your scan tool is lying to you.

  2. #122
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    Sorry i donít think Iím understanding what your saying, your saying if it stays at 600
    My scanner is lying to me? Can you please elaborate? How would it stay at 600 if once i plug in the IAC it should idle it up to the target idle speed set in the chip. Which in my case would be between 650-700 once fully warmed up. If i plug in the IAC and it goes right back to 1k then i know Forsure that the computer is the cause of the 1k idle and not a vacuum leak/ wrong manual setting

  3. #123
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    You are right, it would open up to whatever idle speed is set to in your chip, but the point is, it wouldn't go all the way back up to 1000.
    If it does go back to 1000, then it's something in the computer. If it starts to idle normally however, your scan tool reading a requested idle of 1000 rpm is not true and you know that the scanner is not giving you the right information. If the computer is truly requesting a 1k idle, that is where it will idle if it can. The only real way it has to achieve that is by allowing more air through the throttle. The only way it can do that is through the IAC. If with the IAC all the way closed and disconnected you are still idling at 1000 rpm, there are really only two possibilities. You have a vacuum leak, or the throttle plates are open too far.

  4. #124
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    Ok yes this makes sense, so as of right now it looks like i have to adjust the base idle with the IAC unplugged and then see what it does after it’s plugged back in. I mean unless you have another recommendation? I just want this thing to idle at no more then 700 in neutral (truck is a 5 speed)

  5. #125
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    Run engine til it's warm. Shut it off and jumper pins A and B. Turn key on, do not start. Wait 10 seconds, and then unplug the IAC. Confirm It has closed all the way. You should be able to see the tip if it through the top of the throttle body. Turn key off. Remove jumper across A and B. Start engine and turn manual idle adjustment screw counter clockwise until the idle comes down. Check to make sure that the throttle shaft is actually resting on the manual idle adjustment screw and it isn't bound up in the body of the TBI. Now you should be idling in spec. Shut off and reconnect IAC. Restart engine and see what it does.

  6. #126
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    Is there a way for me to read my rpm’s digitally while doing this? I can’t use my scanner because when it’s in diag mode the rpm’s fluctuate. And i don’t really trust the factory gauge.

  7. #127
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    IMG_2975.jpeg not sure if the pic went through, but yes, coming off the coil there is a white wire with a connector which was/is used for diagnostic tach purposes by gm techs. I used it when I changed my half moon gauges to the needle gauges with a tach. You just need an auxiliary tach. It will give you a true rpm. Oh cool it did.

  8. #128
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    So any aftermarket tach will work? I would like a digital one instead of needle that way i get he most accurate number

  9. #129
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    Another option is to hook up tunerpro with an ALDL to USB cable with a laptop. If you can find a definition file for your ECU. That will give you the computer's reading for what RPM the engine is spinning digitally.

  10. #130
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    I just bought a digital tach from eBay, once i hook it up i will do the base idle adjustment and see what happens. I was going to buy a aldl cable but the manufacturer never got back to me on my
    Question about the cd/usb that comes with the cable so i never purchased it. My
    Laptop doesn’t have a cd drive and the usb option was on back order. I do have the ADX file for my
    Ecu to be able to see live data on tuner pro i just don’t have a cable

  11. #131
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    This manufacture has a thumb drive with there cables. I was in the same boat, no cd drive. It’s where I got mine.
    https://obd2allinone.com/products/aldlobd1u.asp
    Last edited by TriumphR3; 2 Weeks Ago at 04:41 PM.

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