#4831, "Finally got MSII to control stock IAC stepper" Mar-25-10 07:53 PM by Corbin
The MegaSquirt guys finally came out with code that is bug free for controlling a stepper type IAC (a few months ago). That is version 2.1.0 (20090627). I've spent a couple months getting it to work. They "fixed" a few other things that forced me to change several settings unrelated to idle.
I can drop the clutch while rolling up to a light and the engine will settle to a steady idle RPM. I can turn on the A/C and defogger without stalling or bad oscillation. This is a feat with an aluminum flywheel. It does not get hung at high RPM or lose steps after boosting. It is nearly like stock.
Step one is to wire up the stepper motor. Here is the wiring scheme:
MS JS0 = IAC yellow/blue stripe MS JS1 = IAC gray MS JS2 = IAC gray/blue stripe MS JS3 = IAC orange
If you mix this up, the IAC will work in reverse or not move at all. I did solder jumpers across the 1R0 resistors on the underside of the MSII daughterboard. I think that was the only hardware mod inside the case.
Here are my settings:
If your stock ECU is still in place, then it is probably supplying the ground for all of your sensors (under the fuse box, on the body). If the ground for your MS is in a different place, you can get a lot of noise in your sensors when fans or other devices turn on. The latest code is more sensitive and this can cause havoc with your idle (TPS especially). I have my MS grounded to the firewall, where the battery grounds. I chose to run a 4 gage welding wire from the MS/battery ground to the stock ECU ground. That quieted the noise down to a reasonable level. You should play with your VE bins in your fuel map to create a nice flat area right around your normal idle and in slightly higher manifold pressures to cover A/C loading. That will make sure your A/F is stable at idle, loaded and unloaded. It should be slightly rich. I aim for 13:1 A/F, but you could probably go a hair leaner. You will probably want to reduce your ignition advance at idle down to 2 to 6 degrees, mimicing the stock ECU. This creates an artificially weak idle that requires a slightly more open IAC valve. That gives you room to close the valve more and never worry about hitting the valve seat (hitting the valve seat can cause you to lose steps and confuse the MS). I also increased the ignition advance at all RPM below my desired idle RPM. This is kind of an anti-stall feature and makes a nice valley for the idle RPM to settle into.
#4833, "RE: Finally got MSII to control stock IAC stepper" In response to Reply # 0
I’ve been running on closed loop for a while, it has come a long way. If you want the most out of your stepper you should try 3.0.3r as there are some key fixes kens made in the closed loop algorithm on how it engages and saves the last known good steps. Even though 3.0.3 isn’t officially released it’s a very stable code for the 420a. 2.1.1-3.0.3r features better map sampling which makes your idle, cruise, response and a few other things smoother than 2.1.0. I run an ignition advance of 14 with an injection angle of 450 @ 14.5:1 AFR. MS doesn’t lose steps like it use to, the steps are correct from all the tests I’ve conducted on my spare TB. I should also mention that reducing PW at the bottom of the map helps the IAC come to a rock solid idle.
#4834, "RE: Finally got MSII to control stock IAC stepper" In response to Reply # 1
Awesome, Im going to need this soon to hook up my IAC. What are the MS wires though? Mine say SPR1 through 4?
95 Eclipse GS: 10.5:1, Crower 2's and MSII 186 WHP - 150 WTQ 14.697 @ 93.85 MPH......Gone, but not forgotten 99 420A Avenger: Given to my sister 99 GS OZ: Sold 03 Evo 8: Family Car with balls
#4874, "RE: Finally got MSII to control stock IAC stepper" In response to Reply # 3
You did this with Megatune, correct? If Im doing it with Tunerstudios is there something else involved? Ive moved my wires around a few times and I still cant get the IAC to move, and there is an options menu for output settings. Output port pt6 and pt7 are IAC 1 and 2, and they were not enabled. I can enable them, but I also have to set the port settings and conditions.
95 Eclipse GS: 10.5:1, Crower 2's and MSII 186 WHP - 150 WTQ 14.697 @ 93.85 MPH......Gone, but not forgotten 99 420A Avenger: Given to my sister 99 GS OZ: Sold 03 Evo 8: Family Car with balls
#4875, "RE: Finally got MSII to control stock IAC stepper" In response to Reply # 4
Originally posted by 740 turbo brick You did this with Megatune, correct? If Im doing it with Tunerstudios is there something else involved? Ive moved my wires around a few times and I still cant get the IAC to move, and there is an options menu for output settings. Output port pt6 and pt7 are IAC 1 and 2, and they were not enabled. I can enable them, but I also have to set the port settings and conditions.
The "output port settings" are only to be used if you're using the IAC ports as general purpose outputs (GPO's, i.e. relay control). These should be disabled for IAC1 and IAC2 if you're using them for stepper motor idle air controller (IAC) control, otherwise there will be a port configuration error and nothing will work.
#4876, "RE: Finally got MSII to control stock IAC stepper" In response to Reply # 5
Ok cool thanks. I also saw the Fidle in that list to set it up as fan control, so Ill look into that the next time Im over at the garage.
95 Eclipse GS: 10.5:1, Crower 2's and MSII 186 WHP - 150 WTQ 14.697 @ 93.85 MPH......Gone, but not forgotten 99 420A Avenger: Given to my sister 99 GS OZ: Sold 03 Evo 8: Family Car with balls
#4877, "RE: Finally got MSII to control stock IAC stepper" In response to Reply # 6
If I may ask though, Corbin, why do you have the algorithm as always on?
Megamanual: IAC Stepper Moving Only: Powers the stepper only when changes in pintle position are requested. This is the most common type, it holds its position if not powered, and is difficult to turn by hand. Because the stepper/pintle assembly typically has a worm gear, if the pintle doesn't move easily when you try to screw it in or out - DO NOT FORCE IT - you could break it.
IAC Stepper Always On: Powers the stepper at all times. Required if your stepper 'free wheels' when you spin its pintle un-powered with your hand.
15-minute IAC: Operates the IAC is always on for 15 minutes, then switches to 'moving only'. This is sometimes helpful if your IAC operation is erratic.
If that is accurate, my IAC at least would be moving only. And when I did have it connected and set as always on, it didnt move but it did get so hot I almost couldnt hold on to it to disconnect it from the harness.
95 Eclipse GS: 10.5:1, Crower 2's and MSII 186 WHP - 150 WTQ 14.697 @ 93.85 MPH......Gone, but not forgotten 99 420A Avenger: Given to my sister 99 GS OZ: Sold 03 Evo 8: Family Car with balls
#4881, "RE: Finally got MSII to control stock IAC stepper" In response to Reply # 7
I use "always on" to ensure that the IAC will not be moved by vacuum or boost. I can't afford to lose any steps. My IAC does not get hot. The IAC is 15 years old, so I don't really care if I fry it. If I kill the IAC, I will try "moving only". I did the initial tuning in Megatune, but have now switched to TunerStudio. I should probably play with the PID parameters some more, but I moved on to more interesting things.
#4907, "RE: Finally got MSII to control stock IAC stepper" In response to Reply # 8
I finally got MY car to idle reliably using the IAC. I was getting quite stressed about it before but I didnt hit me until I was out toying with settings. I was using Corbins settings, to which my car would idle normal most of the time, but after it got hot it would oscillate pretty bad, 500rpm up to 1500, and repeat. After I started watching the IAC steps gauge I changed my settings, and my PID settings so now my car will settle back down to 900 RPM no matter load, revs, or otherwise. I havent tested my AC yet, but I will do that soon. Im just happy I wont have to keep tapping the gas to get it to stay running.
These are the changes I had to make for my car:
95 Eclipse GS: 10.5:1, Crower 2's and MSII 186 WHP - 150 WTQ 14.697 @ 93.85 MPH......Gone, but not forgotten 99 420A Avenger: Given to my sister 99 GS OZ: Sold 03 Evo 8: Family Car with balls
