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Old 05-25-2019, 02:40 PM   #23
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Originally Posted by amc49 View Post
I normally scream to never touch them too but there can be a reason to do so carefully. If the throttle then begins to hang you back the screw back closer to where you had it.

The engine drops and its' own weight (inertia) drags it down to die if the throttle is not open enough. The actual die point AND THE RATE OF RPM DROP before the die depend on the TB setting. The die point is supposed to be caught by the IAC but the IACs do NOT work as instantly as most think, they take a second or so to kick in the full move and by then the engine can die. It gets to be a problem on older engines and I have absolutely cured dies on mine when say the a/c cuts in by doing that.

When you adjust the butterfly open a bit more you are doing much of the IACs' work by having the airgap already open slightly more, the engine then does not die.

Try it, if you create other issues then just put it back where it was.

Take careful note of how much you move the butterfly, if too much the idle hangs start but putting it right back stops them again.

There is a certain small amount you can adjust there, one way to do it might be to disconnect the IAC at warm idle to adjust TB then, instead of going to the usual 700-750, go to 850 and then plug IAC back up. That should be within the IAC range to still not get 'can't control idle range' codes.

The IAC opens more with a tight TB airgap and closes off some with a wider one, the latter condition is better to have when you have engine falling to die issues. BOTH ways give the exact same 'perfect' idle speeds with engine at pure idle, give THAT some thought.

One day I was simply paying attention to idle bumps and drops and picked up on the fact that there was an electrical 'noise' (like a stepper motor or similar) that occurred a fractional second before the idle actually went up, the a/c clutch was already on (I have a light for that) and I wondered what the noise was. I became convinced you can hear the IAC switch on and then the second later it actually moves to change the idle speed, that second between is your die window. How I came up with bumping the TB butterfly to cure problems, and it worked in my case. No more problems.

The IACs do not work as instantly as we think, they work slower so PCM can stop them on the move at the correct rpm. Why that little die window can be there.
I'll give it a go. [emoji106]

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