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.

The changes are here:
http://www.msextra.com/doc/ms2extra/changes2.1.0.html
Generic documentation is here:
http://www.msextra.com/forums/viewtopic.php?f=91&t=30441&sid=84c8a3d2dc5c138aa7497cdf3ba86199

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.

Corbin
'95 ESI-T

Now with more power and fewer leaks



Humble servant of the Wiki

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.

Awesome, Im going to need this soon to hook up my IAC. What are the MS wires though? Mine say SPR1 through 4?

Congrats Corbin. I have been following this for a while as well. The Neon guys are an incredible help on it.

This will prolly be the next project after the Mopar is done.

Terry

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.

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.

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.

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.

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.

Corbin
'95 ESI-T

Now with more power and fewer leaks



Humble servant of the Wiki

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:

i have the stepper wires , and im about to wire them out. My wires are diff then above..they are: spr1 - spr4 how does that relate to above? thanx

Please refer to the last post of this thread:

http://forums.2gnt.com/dcboard.php?az=show_topic&forum=54&topic_id=4936&mesg_id=4936&page=

i did, but my outputs for stepper are differnt,

Well, after searching for 2 days on every site I could, I can't get a clear answer, so I'll just ask.

I have a version 2.2 board. How would I hook up my IAC to this?

EVERYTHING i have been finding has been for a V3 board.

Thanks for any help you can provide.

Brian

Originally posted by ForceFed420a
Well, after searching for 2 days on every site I could, I can't get a clear answer, so I'll just ask. I have a version 2.2 board. How would I hook up my IAC to this? EVERYTHING i have been finding has been for a V3 board. Thanks for any help you can provide. Brian

Is the board already set up for stepper motor IAC control, or are you asking how to do that?

There's a lot of information here: http://www.megamanual.com/ms2/IAC.htm

Paul,

Thanks for that link! In all my searching, I didn't see that. No, the board is not wired for IAC, and everything I had come across was either for the version 3 board, or the software settings that I needed to set--neither of which helped. That page was the missing link I needed for the hardware mods.

Oh, one more thing. The reason I didn't come across that link was because I was searching the msextra site. Will this mod still work with msextra code?


Thanks again for your help,
Brian

Originally posted by ForceFed420a
Oh, one more thing. The reason I didn't come across that link was because I was searching the msextra site. Will this mod still work with msextra code?

Yes, the hardware is the same for either code version.

Paul,

Excellent. Thanks very much for your help.

Brian

No problem, I'm glad I could help.

Ive been toying with the settings for my IAC and I have an almost perfect idle (again). This is a lot easier than it was last year. I also just today changed my close delay from 3 seconds to 0 (meaning do not close) and the car responds to part throttle SO much better. When its still cold it has to open farther to idle where I want it to, about 60 steps, so when I tap the throttle it jumps a little high. After its warmed up it will sit about 35-40 and a very light throttle tap (2-3%) raises the throttle by a few hundred RPMs, and when I let off my dashpot adder stabilizes it and PID takes over. When I had the IAC closing when the throttle was depressed, a throttle tap would send the RPMs high and slowly settle to a normal 3% as the IAC closed. And also, taking off in 1st gear you could feel the car surge and see it go lean from the IAC being open until it closed to where my VE table was set at.

After setting IAC to do not close and a quick retune, my car now idles, takes off, and cruises better than it EVER did with the stock 95 ECU. I would recommend others at least try the do not close option if the car doesnt like very low RPM or taking off in 1st.

Interesting. That is probably about the only thing I haven't tried. I've been closing the valve to retain some engine braking. I've been dicking with IAC settings and ignition advance for a year now. It has been really hard to get a stable idle that also reacts fast enough to A/C compressor engagement and doesn't stall when you put the clutch in while engine braking to a stop in 25F to 105F weather.

Corbin
'95 ESI-T

Now with more power and fewer leaks



Humble servant of the Wiki

Thats what I thought about the engine braking too. But then I thought it out, when you let off the throttle to let the overrun fuel cut engage, the IAC will open to its last good position + dashpot adder anyways, (usually about 45 for me). Do not close is doing the same thing, but instead of closing while driving and opening on let off, its staying what it was while in PID control and adding the dashpot when you let off. For me it required playing with the step adder number but its working very well now.

Guys, I have been trying to get my IAC to work as smooth as you, but I'm not having much luck. Are you still using most of Corbin's settings, or have you found settings that work a little better? I'm thinking mainly the:

Step size
start value
open steps
closed steps


I can figure out the rest of it, but if someone could supply those numbers (assuming they've changed in the last couple years!) I think I could be on my way.

I'm doing some further testing today to verify it's not a hardware issue.

Thanks!
Brian

Bringing this thread back from the dead! lol BUT can some one put in perspective on how the PID works with the idle. i just dont seem to get the full picture on what its for?
And what are the benefits of running "closed loop" idle control?