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Old 06-15-2004, 02:28 PM
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350 TBI idle and timing questions

After looking around and not seeing what I want to know I've decided to ask two questions. I'm busy with a SBC 350 TBI motor with aftermarket programmable ECU.

1. How do I adjust idle speed if the ECU doesn't have the capability?
2. (Dumb question) How do I adjust the base timing on this electronic dizzy? (I know how to do it with a points dizzy)

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Old 06-15-2004, 02:36 PM
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To properly set idle you would follow the directions for resetting the IAC Valve. If I remember right they go something like this. 1. Jumper the A & B connections on the diagnostic link with a paper clip or what not. You'll hear the IAC screw resetting. 2. After 30 seconds unplug the IAC valve. 3. Fire up the engine and using the idle adjustment screw somewhere on the throttle body, adjust the idle to where you want it. 4. Shut down the engine and clear the codes in the computer by unplugging the negative side of the battery for about 5 mins (some computers take 10 seconds to clear, others a couple of minutes). 6. Take the jumper out of the diagnosis link, plug the IAC valve connector back in, and put the battery link back on. Fire it up and let it run for a couple of minutes. It should be set.

For timing (which I would recommend doing before setting your idle) there should be an EST (Electronic Spark Timing) disconnector most likely somewhere near the brake booster (but it varies). You need to unplug this to bypass the computer. Once this is unplugged you can set base timing. After you set base timing with the engine running, shut it down, and unplug the battery to cleared out the stored memory. Plug the EST connector back in, battery back on, and fire it up and it should now have your setting as base timing.

I hope this helps. If you get stuck, research on google and you should find some more help, or just ask any more questions and im sure someone more knowledgeable will be able to help.
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Old 06-15-2004, 07:00 PM
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What kind of EFI system?

So long as your throttle body hasnt been messed with there should be no reason to reset base idle speed. The adjustment screw is under a hardened steel cap its on lower left side front of throttle body, but not easy to get out.

Since the IAC is a stepper motor either you need a special tester to force it to move or hook it up to another truck with working computer system.

On the stock set up you can trick the computer into fully extending the IAC pintle by creating a temporary vacuum leak then quick unplug the IAC solenoid. Make sure you have it installed you dont want it to extend too far.
Once this is done.
If idle speed is above 800 RPM check for vacuum leaks and check adjustment of throttle stop screw on throttle body.
If idle speed is too low adjust stop screw until idle speed is 600-700 RPM.



Did you know that the tbi distributor can be made to run without the computer on its own little preset advance curve by disconnecting the 4 wire connector? This is a common marine ignition system.

There isnt a lot of timing built into the module but it would make for a very simple ignition system if you wanted to run a little more initial timing like a person would when running a big cam. The stock GM module has a pretty abrupt advance curve but I think the aftermarket marine ones are a little better.

Base timing can be set by using a connector that has terminals jumpered and connecting one of the others to bat+.
I can send you instructions on how to do it.

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Old 06-16-2004, 12:50 AM
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Thanks

Thanks Greg,

I'd appreciate if you could send me the base timing instructions. Can those instructions be used with the motor not running as the dizzy still needs to be put back and that's why it will need base timing to be set once it's back.

Please remember guys, this engine is not in a car currently and is going into a 53 Chevrolet. There is NO factory controller and I'm therefore using an AFTERMARKET laptop programmable ECU. It doesn't have an idle speed control function so I need to do the idle speed manually.
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Old 06-16-2004, 02:56 AM
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Oops . . . tbi not a tpi. I shoudl read more closely.
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