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

[Jay Vessels]

Hi there!

If you're setting minimum air (throttle stop screw) so it idles at 700 
RPM, then that should be less than the minimum idle speed in the cal. 
One accepted way to set minimum air (once the idle speed is set properly 
in the cal) is to adjust minimum air so you get about 2-3 IAC counts at 
hot idle. The GM procedure usually gets you to about 30 IAC counts, but 
some think moving as much air through the throttle body as possible (in 
TBI apps, anyway) is the better choice. .

You want the IAC to have a bit of headroom, though, so if your cal's 
idle speed is under 700 RPM, and you're setting minimum air higher than 
that, the ECM is no longer controlling the idle speed.  Not good.

If you're getting stalls and you've got the VSS connected, then you may 
not have minimum air adjusted properly, or you've got some tuning to do. 
  Assuming the low RPM timing/fuel is right (i.e. the fueling at low RPM 
isn't going to just drive it to a stall), either the IAC doesn't have 
enough headroom (you need more IAC counts at idle) or you need to get 
more aggressive with the IAC tuning.  Unless you have a lumpy cam, I'd 
guess the IAC constants are fine.

The sky-high idle after a stall is apparent in the TBI code ('747, '429, 
etc.).  I don't remember if it's in $A1 or not, since it's been a while 
since I drove a 5-speed $A1 car.  The most annoying thing in $A1 for me 
was shift-assist which to me looked too much like a throttle hang.  I 
managed to tune most of it out, but I never got it 100% like I wanted it.

Jay Vessels
1982 Chevrolet S-10 Sport, 2.8V6 TBI
1984 Chevrolet S-10 Blazer Sport, 2.8V6 (TBI pending)


Gary Evans wrote:
> I do have VSS input - it happened anyway. Never had the problem with the 
> sky high idle, but I am running $A1 code which might be the difference.
> 
> 
> 
> On Apr 5, 2007, at 1:15 PM, Tomas Sokorai wrote:
> 
>> On 4/5/07, Gary Evans <gary at garyandliz.com> wrote:
>>> 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.
>>
>> I had that problem in a BMW I6 with '7727 + $8D setup. It's because
>> you don't have proper VSS input.
>> I ended doing the IAC setup, so the idle was almost my desired idle
>> too because a VSS was too difficult to install.
>>
>> The only problem I couldn't solve, is the sky-high idle when you stall
>> the engine and then try to restart right away.
>>
>> --Tomas J. Sokorai Sch.
>> _______________________________________________
>> Gmecm mailing list
>> Gmecm at diy-efi.org
>> Subscribe: http://lists.diy-efi.org/mailman/listinfo/gmecm
>> Main WWW page: http://www.diy-efi.org/gmecm
> 
> _______________________________________________
> Gmecm mailing list
> Gmecm at diy-efi.org
> Subscribe: http://lists.diy-efi.org/mailman/listinfo/gmecm
> Main WWW page: http://www.diy-efi.org/gmecm
>