[Gmecm] IAC / AIS Setup - $8D/7730 )

Fri Apr 6 03:26:54 UTC 2007

Thanks for the input, guys.  That's pretty much exactly what I'd hoped to
hear.  I also like the "bonus feature" of not having the ECM cover for a
vacuum leak, although (knocking wood) I can't recall the last vacuum leak
problem I had.  This evening I reset the idle via the throttle plates to
800rpm, and I'll let the IAC handle the cold startups and A/C=ON situations
for me, as it should be.  Didn't get to re-test with the IAC hooked up
again, as I had to put Monkey Boy to bed, and his room faces the garage...
Tomorrow, I guess.  The only potential down side I can see is if idle speed
creeps up appreciably when hot.  I won't have to wait too long to test that
situation here in Texas.

I think another bonus will be that the IAC will be quieter, as in not
whistling from time to time.  It gets pretty annoying hearing the IAC
whistling over the engine, and I'm not sure what it must sound like to the
cars around me in traffic.  I'm using the old Mopar "unsilenced" air cleaner
housing, and it really doesn't muffle a screaming IAC very well at all.

FWIW, the pintle was still allowing a slight amount of air to pass, I could
feel the vacuum on my finger when I covered the port on the top of the TB.
It made maybe 20-40rpm difference, as best I could tell.  I'd need a more
accurate tach to know for sure.  My hand-held only reads in 10rpm
increments, and my dash tach has 100-rpm ticks on the face.  For that
matter, I need several more accurate gages, as my Autometer vacuum/boost
gage reads a solid 15" vacuum, but the large DIA vacuum gage I had been
tuning with says 12.5" at idle.  Maybe I just need to calibrate all my junk
one of these days.  I wish I knew which gage to trust, that's a SIGNIFICANT
difference, right where it's important.

Clair

----- Original Message ----- 
From: "Gary Evans" <gary at garyandliz.com>
To: <gmecm at diy-efi.org>
Sent: Thursday, April 05, 2007 2:33 PM
Subject: Re: [Gmecm] IAC / AIS Setup - $8D/7730 )

> I agree with Duncan - I had a similar expereince with my setup (dual
> 3.1 ecms on jag V12). The car would sometimes stall during decel
> because IAC counts could drop too low while the car was moving.
>
> Set the throttle plate to provide the minimum *desired* idle speed
> (e.g. 700 rpm), not the minimum possible idle speed. This will give
> the IAC the most room for adjusting the idle speed upward.
>
> Bonus feature of this setting is that if you develop a vacuum leak
> you will be alerted to it by a too-high idle rather than allowing the
> IAC to compensate and cover up a potential problem.
>
>
>
>
> On Apr 5, 2007, at 12:19 PM, Cowen wrote:
>
> > I know the IAC setting procedure varies, and I've seen
> > it described different ways for the same car (but from
>
> > different sources) too.  That said however, I've got a
> > 7730 in my cobbled together system, and what you
> > describe is very different from what I've read.  In
> > fact, what you've described caused serious problems on
> > mine when I first got it going.
> >
> > I'm using a throttle body from a 2.8l, and an an ECM
> > from a 3.1l, onto a 3.4l.  The point is, when I
> > initially started it, the throttle body was set to run
> > a 2.8l fine.  Now, for a given RPM, a 3.4l requires
> > more airflow than a 2.8l. (3.4-2.8)/2.8=21% more air
> > required.  Wow!  Although the IAC compensated, it
> > didn't run well.  It felt like it had no torque,
> > requiring high revs start the Jeep moving.  It had a
> > huge bog on acceleration.  The reason?  As my foot
> > advanced the throttle, the ECM was closing the IAC -
> > and the two efforts canceled each other out!  Simply
> > resetting the butterfly in the throttle body made an
> > incredible improvement!
> >
> > Now, consider how you've set things up.  Your idle
> > should be about 700-750, but you're setting the
> > butterfly for about 400.  Best case scenario,
> > (700-400)/400=43% The IAC must provide 43% more air
> > than the butterfly to get the idle at 700!  If your
> > setup works anything like mine did, it's no wonder
> > things aren't working right!
> >
> > Solution?  If I recall, this is the procedure to set
> > it with your 7730:
> >
> > 1. Jump the pins on the ALDL to trigger MIL flashes.
> > 2. Key On, Engine Off.  These two steps force the IAC
> > pintle to extend fully, so IAC can have no effect on
> > idle.  You should hear the IAC running, trying to
> > extend the pintle forever!
> > 3. Unplug IAC.
> > 4. Key Off, remove ALDL jumper.
> > 5. Start engine (may require a foot on the gas if
> > butterfly is really closed), and set butterfly to
> > provide 700RPM idle.
> > 6. Reconnect IAC.
> >
> > Good luck!
> >
> > Duncan
> >
> > **********************END TRANSMISSION**********************
> >
> >
> >
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