So...after about 3 hours of testing and manual tuning, about 25 tunes later I finally got a good grasp of just how the idle control system in the dodge system works. First of all, this guide is meant for those who try all the factory settings for the IDLE ETC control and still find themselves with an unstable and surging idle. ALWAYS try the factory settings first before going about changing anything, for most setups they will work ok or only need slight tweaking.
Ok now onto the tuning. First of all, everyone should take 15min to read the following couple of links. While not the same as GM setups, the concept is already there and laid out OK, though I found in general research of a proportional derivative integral (PID) controlled setup the order of magnitude for each of the three adjustments is actually a little different.
GM Link (read under each of the Proportional, Derivative, Integral sections about the High and Low settings, we don't have filters)
https://www.hptuners.com/help/index...._tm_engine.htm
The ol' Wikipedia:
https://en.wikipedia.org/wiki/PID_controller
Another helpful "tuning" link:
http://www.expertune.com/tutor.aspx
So after sifting through that info, you are still probably going, WTF did I just read?? Haha, I know I did after the first time. Let me try to explain it a little more simply, then go back and read Wikipedia link again, it makes the most sense for our application.
Our System
Dodge employs two PID controllers to handle getting rpms to your target rpm, one for timing advance and one using your throttle body, it uses both to get things under control. In standard setup, the timing advance PID controller is capped at a maximum of your PT timing table and can only go down from there. It will pull timing back as rpms go above desired idle down to your SPARK>ADVANCE>Min Spark TqRed or to the point where the torque the PCM calculates is being pulled hits the maximum allowed (more on this later), and will go up to a max of your PT timing table or to the point where the torque it is ADDING hits the max allowed in the tune when the rpms fall below desired idle.
Throttle body PID controller has no such cap, it is all setup by the max/mins of the idle tables in the IDLE ETC tab. The throttle body PID controller will be your biggest influencer to a surging and hunting idle, it has the least amount of control and is the most sensitive to being out of tune.
PID Basics
Ok so now you understand you have two PID controllers, they compound each other and act the same way using two different adjustments, timing and throttle body (aka airflow). Easy way to understand the three aspects of the PID controller is as follows (from here on I will call each component just by P, I, or D):
Proportional Gain: This is the most basic of the three, this is simply a table of how much torque to pull or add given a certain RPM error. It has very little chance of ever getting control of the idle on its own, BUT it is important to understand you HAVE to make the rpms overshoot to begin with, setting the edges of the table (1000 rpm error) too small will result in a sputtering slow rising rpm on startup and instant stall every time you come to a stop, or if it doesn't stall a HUGE swing up and down surging. If you simply removed all of this control you will almost never get the rpms to rise up to your desired idle. The strategy is to make it overshoot but then quickly using the I adjustments and then finally D adjustments get it to stabilize as quickly as possible.
Integral Gain This is the next adjustment in the over and under error to start getting the idle to settle down. Think of this as the adjuster for HOW LONG the rpms were either above or below the desired idle, but also cares about just HOW much as well. So very fast surge happening within a half second of going above and below the desired idle will need a smaller integral adjustment than a very sloooowwww up and down surging that takes a full second to go from negative to positive. The NGC PCM doesn't really display the adjustment to us this way, it simply shows us an error rpm and amount of torque to remove or add just like the P table, but in concept it works the same way. The strategy in tuning this aspect is to make the PCM pull back on the P adjustments in opposite directions to start SLOWING down the over and under shoot of rpms. It also serves to fix the "offset" you couldn't fix during proportional. Basically you are going to find your up and down surging centers around a point lower than your desired idle, integral brings the entire curve upwards.
Here is an example of the two in play...
If the rpm error is -200rpms (Idle desired of 900 and rpms hit 700) the P adjustment says add +10ft/lbs of torque, it results in rpms flying up to +200rpms over idle to 1100 then P responds with -10ft/lbs to bring rpms back down, rpms fall back to 700rpms, starts all over again...the integral will say ok you over shot by 200rpms on the way up and down and it took about 0.50 seconds to complete the up and down, and with the same command of torque adjustment on the next cycle you are going to overshoot by 200rpms again, tone it back by 5ft/lbs and lets just add 5ftlbs but change the rate you apply the 5, apply it very fast but also dial it back quicker to 0 quicker once near target idle and go -5ftlbs on the way down quicker since P took so damn long to complete the last cycle. I is accumulative of the past errors, so have to be careful, if you command too much the "sped" up rate of the increase/decrease can cause the same overshoot. If done correctly the adjustments of both P and I will get smaller and smaller and eventually come close to zero.
Derivative Gain This is the final adjustment, best way to think of D is it a predictor by studying the slope of the ups and downs over time as P and I work together to get the idle stabilized. So if on the first up and down the slope was 2, on the next it was 1, then the final it was close to 0, derivative will try to take those errors and adjust over the top of P and I so that you get the up and down of that third cycle pretty much right at the start, eliminating the up and down right at the start.
Here is by far the best visual of how each function, notice in the legend the gain being changed (Kp is proportional, Ki is integral, Kd is derivative)
https://en.wikipedia.org/wiki/PID_co...n_Animated.gif
PID_Compensation_Animated.gif
More to come.....