Wondering which way has shown to have the best results with warm up and reliability. I pulled my throttle cable back so that the throttle ~3-4% open at idle.

This technique makes the low rpms when coasting to a stop a bit shakey and makes the idle slightly choppy.

In megatune, i can see the throttle fluctuate between 3-4%.

There is a working PWM idle code in the current extra code, but you will essentially need a very large boost controller valve. I think Matt tried this with a boost controller once and noticed that it doesn't have enough throughput. Maybe a nitrous valve would work better...? I've never played with a nitrous system before so I don't know how big they are.

The MS2 has a nice GM stepper motor idle valve controller (very similar to the stock Neon one) chip built in but the code to run it isn't exactly 420A friendly yet. There are a few people scattered about working on converting the extra code but no one with the skill seems to be very interested in doing it. The problem is that the extra code has been written by many people, each person would have to convert their segment to the new C language, or someone/a team would have to learn how the entire program is written. The code is about 13,000 lines of assembly (around 1430 lines compiled) right now. No one wants to deal with that on their own unless they have way too much free time or are being paid to do it.

If you leave the stock ECU hooked up it will really mess with the idle valve especially if you don't have half of the stock sensors attached to it or have resistors on them like me. It kind of sits there, stabilizes, but when you go for a drive it will open and close the valve very quickly attempting to the engine back to idle. It makes driving very unpleasant. If you leave it unhooked, your idle will be slow when the engine is cold and fast when it is hot, and if you throw boost pressure on it the idle valve will be forced open and you will have to plug it back in for a short period of time so that the stock ECU can re-adjust it back. Very annoying.

Do ou think a manual valve would be helpful?

the poor ECU. i wonder what it must be thinking as it loses more and more control over the engine.

how difficult would it be to retrofit a different IAC motor into our mani? what kinda flow does the IAC typically see? i would think if you were using a solenoid of some sort it wouldn't be that difficult to attach it to a vac line - effectively creating an electronically controlled vac-leak... which is really all an IAC is when you think about it... you wouldn't even hafta connect it to the intake - just slap a mini filter on the inlet to the solenoid. oh and a check valve for boost.

maybe i'm oversimplifying the problem though. :shrug

Two stage solenoid? Maybe a push button?

push button in for cold operation, push out for fully warmed up operation?

What soleniod/s would flow enough air to keep it idling?

Originally posted by rs-pssst
What soleniod/s would flow enough air to keep it idling?

Not sure... There are lots of 'noids on the market but the first thing to find out is how much CFM the engine needs at idle because most of that flow will be going through the 'noid.

Maybe someone with a similar displacement engine and a MAF could measure the value at idle and that would be a good ballpark to start at.

Yeah i've had quite a bit of time trying to get the idle issues worked out, but so far i've only come up with this as a temorary solution...

I removed the stock IAC, and then drilled/tapped the pintle hole in the throttle body for a bolt. I used a larger washer on the bolt that perfectly fits inside this larger diameter part on the TB where the body of the stock IAC fits against..its kinda hard to explain it..I then sealed that with RTV. So now, the IAC bypass air passage is blocked off, and idle is now controlled by the throttle plate. There is a thin metal cap covering the throttle stop screw, and I just turned that out to raise the idle to the right RPM when fully warm. When the motor is cold, you have to put your foot on the gas pedal just a little to fire it up, and keep it on the gas for like maybe a minute or so. After that, it idles a bit low until its fully warm, but the idle is very stable, almost better than stock. I use around 13 degrees of timing at idle, and run it a bit rich into the low 13's, as this helps to keep it idling when cold without using the gas pedal.

There are mechanical/electrical air bypass valves on some Volvo cars, that let extra air into the engine when cold, and as it warms, closes it off slowly. This would be the easiest form of an IAC, which needs no connection to the MS.

other than warmup is there really any reason to even need a means of controlling the IAC if you have a set volume of air getting to the engine? i know the stock ECU likes to fiddle with it a lot and run various diagnostics... but if you can get your idle rpm set appropriately with some sort of bleed valve (or keeping the throttle plate from closing copmetley like xtreme said) then it's just a matter of getting increased airflow for warmup, right? there's not really a need for actual IAC control persay, right?

Yeah, the throttle plate fix and a simple Fast Idle Valve would work great. That way you wouldn't need to keep your foot on the gas when the engine is cold. The fast idle valve closes when the idle starts to really go up (engine is warm) and the slightly cracked throttle takes over from there.

Originally posted by MCubed45
other than warmup is there really any reason to even need a means of controlling the IAC if you have a set volume of air getting to the engine? i know the stock ECU likes to fiddle with it a lot and run various diagnostics... but if you can get your idle rpm set appropriately with some sort of bleed valve (or keeping the throttle plate from closing copmetley like xtreme said) then it's just a matter of getting increased airflow for warmup, right? there's not really a need for actual IAC control persay, right?

Well this can be subjective to a point..just depends on what you really want out of the setup. If you want it to be perfectly like stock, then you will need more than just extra air at warmup. I've noticed with my setup, that when revving the engine, or just coming to a stop, the rpm will drop below idle speed-kinda like the motor wanting to die out, although not that severe- and if you have A/C and want to use it, it may drop your idle speed too low. This means you will have to run prob close to 1000 rpm idle speed, which is really what i'm running about now. So basically, the MS will never have the smootheness of the stock ECU and IAC, but we can get it pretty close if you are willing to deal with these few issues.

I have a cammed 2.4L and my idle is dead on. All i did was adjust the idle stop screw to keep the throttle open a touch, and adjusted it to find that sweet spot where the IAC is almost completely closed to compensate but not closed enough to throw a code for the IAC (25). Once the car is warmed up, it idles steady at ~1000RPM, doesn't seek, doesn't stall on decel, but has the same slow idle return issues under cruise that all 2GNT's have. It took me five or six times to get the fine adjustment I needed to take most of the idle control out of the ECU's hands by keeping the idle air pintel deep in its lowest idle adjustment range.