[Diy_efi] idle control 1227747

Darryl M Gilbert dgilbert78
Thu Mar 9 03:55:30 UTC 2006

David: Ok on all. Yes I am just playing with the table you mentioned.
>From what I understand that is suppose to be the FAST IDLE table, then
when temp gets to a particular point the TARGET idle table is suppose to
be invoked, but its not really clear how it all works. No matter how I
play with the idle adjust screw the ECM wants to attempt to keep it
running up a little over 1000 RPM. I can fool with the idle stop and
drive the IAC counts down to zero, but when it is at 0 this simply means
it is out of range. The IAC steps should really never get to 0, because
once they do the ECM can no longer control the idle anymore. I am trying
to get the IAC counts down to maybe 10 or so at desired idle. From what I
read the lower the better at idle, but never 0. I will play with the
table you mentioned
thank you
On Wed, 8 Mar 2006 21:20:48 -0800 "David Allen" <davida1 at hiwaay.net>
>   This can be confusing and I am not the expert but... I did have the 
> same
> problem and did finally figure it out!
>   I'm assuming this is a newly injected engine converted from carb?
>   If the engine had a vacuum leak or if the minimum airflow (idle 
> stop screw
> on TB) was too high, the ECM should show the IAC counts at "0" as it 
> closed
> the IAC fully trying to bring down the speed.
>   Ideally you want the IAC nearly closed (0 steps) when idling at 
> base idle
> warned up. This way most of the air enters around the throttle 
> blades and
> you get better fuel mixture distribution.
>   When adjusting my car, it would not idle down until it was almost
> borderline overheated. Under normal conditions, the IAC counts would 
> never
> drop all the way to 0 even if I created a big air leak and sent the 
> RPM to
> 2000.
>   I had to reduce the values in "IAC steps vs. coolant temp" table. 
> Using a
> real-time tuning device I gradually reduced the table across the 
> board until
> the engine ran at the specified speed. If the "IAC steps Vs. coolant 
> temp"
> values are too high it will prevent the ECM from locking in on the 
> desired
> idle RPM constant. To get a high-compresson, roller cam 305 to idle 
> down I
> had to reduce the values by about 5 (if I remember correctly). In 
> addition,
> the main spark table can have the timing reduced around the idle 
> region to
> help smooth and slow the idle.
>   Hope this helps, and hope someone with more insight can 
> contribute.
> David
> > Hello: 1227747 355cu in SB Chevy. Trying to figure out how to get 
> idle
> > down to the idle speeds in the target idle vs coolant table. 
> Currently
> > ECM wants to keep the engine running approx 1100 RPM, with 80 IAC 
> steps.
> > Temp is at 171 deg F. TPS reading .51 volts at idle, but Idle 
> speed will
> > not come down to target idle table speeds?? Is there a switch that 
> tells
> > the ECM when to invoke the target idle table?? I think IAC steps 
> vs
> > Coolant is for Fast Idle when cold?/ Any help will be greatly 
> appreciated
> > Darryl..
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