How do I Tune Idle when Running Out of IAC Count Range

[Matt_lq4]

Ed, I'm enjoying the hell out of your amazing tutorial package. I pretty much own all the training materials available, and yours is by far the most comprehensive and detailed I've seen yet.
All the material is truly professional quality and presented with thorough explanations of what is truly occurring when making changes. I have found that knowing how it all fits together and rules
of thumb are a lot more valuable than having a recipe list of changes to make. One of the most valuable features of your tutorial is that it provides an excellent presentation of the evolution of the
GM PCM, including the changes GM has made in the way the various PCM's control LS motors and precisely how this impacts the approach to tuning for each version of their PCMs. I would suggest
that you consider showing what you have to James Short, if he has time to look it over, simply because any feedback he may provide should prove valuable to your product. Have a great holiday
weekend my friend!

X2 I also have Ed's tutorial booklet and love it

[JamesLinder]

Thank you for your advice Steve!

[JamesLinder]

This is pretty much exactly what I learned in dealing with my car. I had to have my TB blade wide open for cold starts, and yet
I still ran out of counts with AC on in gear. I was able to re-calibrate the IAC counts versus area table yesterday where I had
control on both ends and idle behaved well, however at idle in park (low load condition) I noticed that desired airflow was still
a little less than dynamic air, so I guess there is still some improvement possible. When blipping the throttle to 2500 rpm and
letting off it returns to 950 RPM extremely smooth and without any swings below or above the set point. My question now is
does desired airflow have to be exactly equal to dynamic airflow. I did notice is that mass air flow (SAE) and dynamic
airflow are nearly identical at all loads.

[JamesLinder]

When I finished calibrating yesterday IAC counts were 70 at idle in park with AC off. In gear with AC on was 230 counts.
In park with AC on and in gear with AC off were between these two. Cold idle starts are robust now with the increased
air available in the IAC circuit.

[JamesLinder]

With enough time and effort I have achieved excellent idle from freezing weather to hot weather. But I have had hundreds of hours to
tune my own car for several years in all types of weather. This is not possible when you have to tune a customer's car in a day or two.
I believe the key is buying the best made parts that give you the best start, such at the PTM throttle body and the TSP MAF from Texas
Speed and Performance. Since the MAF has straitening vanes and the PTM TB has well designed IAC port system to begin with, you
are miles ahead when you start tuning. Given my cam is the MS3 (238/242 duration at 0.050) and 10:7 to 1 compression, having a
very stable idle at 950 RPM at all ambient temperatures has not been all that difficult to achieve, I believe this says a lot about the quality of these components. I had to use 22 timing advance for idle in park and 30 degrees for idling in gear, and only minor tweaks to PID air settings. I do not mind sharing my tune if anyone would like to see it.

[mowton]

James,

Thank you for the props and glad your idle is under control....I had been working on a tool to include in our tutorial which I posted in your other thread. Perhaps your effort to get you idle in line would be a good set of data points to check its accuracy or even effectiveness....Here it is if you have the time...

Thanks again to you and Matt for your kind words.

Ed M

[JamesLinder]

Thanks a million Ed! I will give this a try either today or tomorrow and post the results.

[mowton]

Thanks a million Ed! I will give this a try either today or tomorrow and post the results.

Cool....I don't have a DBC available very often (remote tuning doesn't afford me the luxury of R&D unfortunately) so if you could maybe send me some iterative logs you took while zeroing in on the finished product it would help me test some theories/work sheets. Asking that is a lot but I would also need the IAC Effective area table that supported each log....sorry. If not, no problem.

Getting ready for a family BBQ :-) enough tuning til tomorrow...have a good holiday

Ed M

[LSxpwrdZ]

James, not sure how opening the hole reduces the IAC count globally. If you needed more air to idle hot and you had to increase the number of steps to open the blade then you would lose dynamic range to handle the cold start....enlarging the hole/closing the blade a bit and getting back those steps would then increase the range...no?

I like the timing idea, never thought about that :-)...I did see than Dan M use timing in idle control recently...

Ed M

His problem wasn't that he needed more airflow at hot idle, it was that his IAC wasn't affectively adding the amount of airflow per step that it needed to deliver the idle needed when loads are placed on the engine (AC, In Gear). His idle counts were already zero at warm idle in P/N. Opening the throttle hole would bleed more air into the manifold however that would also force the IAC to close back some to compensate or bring IAC counts down. If he's already at zero counts in P/N opening that hole would make the engine idle high.

If the car idles in P/N at zero counts but pulls up to over 100 counts when put in gear or the AC is engaged then the IAC passages aren't adequate enough to idle the engine. There shouldn't be more than a 50-70 count swing from hot idle no load to hot idle in gear with the AC on.

On cars that have tight stall convertors with decent size cam's you sometimes will even need to bump the "in gear" idle spark table some to help compensate some of that TQ.

[mowton]

His problem wasn't that he needed more airflow at hot idle, it was that his IAC wasn't affectively adding the amount of airflow per step that it needed to deliver the idle needed when loads are placed on the engine (AC, In Gear). His idle counts were already zero at warm idle in P/N. Opening the throttle hole would bleed more air into the manifold however that would also force the IAC to close back some to compensate or bring IAC counts down. If he's already at zero counts in P/N opening that hole would make the engine idle high.

If the car idles in P/N at zero counts but pulls up to over 100 counts when put in gear or the AC is engaged then the IAC passages aren't adequate enough to idle the engine. There shouldn't be more than a 50-70 count swing from hot idle no load to hot idle in gear with the AC on.

On cars that have tight stall convertors with decent size cam's you sometimes will even need to bump the "in gear" idle spark table some to help compensate some of that TQ.

James,

Thanks for the detailed explanation. I was looking at this bass ackwards...assumed the added air from the blade was accumulative over the dynamic range of the steps....it is not! It only establishes a new starting baseline which further exacerbates the issue while the granularity of each step remains the same...the solution is more air per step and the only way to do that is increase the pathway...

Thank you again.....never too old or too smart to acquire new knowledge and insight :-)

Ed M

[mrvedit]

With plenty of people running the FAST LSX(R) manifold and FAST 102mm throttle body, I had hoped to find the "IAC Steps vs Effective Area" for this TB and the "Transient Fuel Mass" tables for this manifold, but cannot find them. Has anyone calculated them and made them available anywhere?
I see mowton's spreadsheet for calculating the IAC Steps table, but am hoping someone has already done this for the 102mm TB and can share it.
Thanks.