idle air control...When?

[Fueler]

A bit of a general question.
What combination criteria or tuning issue determines when a Idle air control should be added?

Thanks

[muythaibxr]

You'll have to be more specific.

Do you mean when should you turn on the feature and use it? Or are you asking when the code turns on idle air control?

Ken

[Fueler]

neither actually.
I will try again.
When purchasing parts for a new setup is there certain engine types and TB size/type that require IAC and other's that do not?
Looking for a rule of thumb I think.

[elaw]

To perhaps overgeneralize a little, all engines require idle air control in one form or another.

It's possible, especially with smaller engines with few or no accessories, to create a setup that works okay with the idle completely fixed. Lawnmowers and such and some motorcycles are set up that way, but those engines usually aren't expected to idle properly until warmed up.

But even carbureted car engines have "idle air control"... typically in conjunction with the choke there's a cam that increases idle speed when the engine is cold. Then you have the challenges of keeping idle speed constant as load changes - A/C turns on and off, electric cooling fans cycle, and so on.

So IMHO 99% of the time on a car engine you're going to want some way of having the Megasquirt control idle speed. Obviously you have to start with the proper hardware, then for a simple setup you can use open-loop control. For tighter control at the expense of some tuning effort, use closed-loop.

[dontz125]

An IACV is usually the easiest way, but some have reported (reasonably good) success with a fixed idle screw and careful tuning of the idle advance and VE table down at the bottom.

[TheSilverBuick]

I ran my Firebird L6 engine without an IAC valve for a while and used ignition timing based idle control. It worked reasonably well other than at times it struggled to stay running when extra cold. I've since added an IAC valve and cured the cold start, but the ignition timing control could swing the idle speed by a couple hundred rpm, which I basically took a warmed up engine and turned the throttle body adjustment screw to open the throttle while the MS3 backed timing off to maintain targeted idle speed (you have to temporarily set the TPS reaction to like 50% so it doesn't pull out of closed loop) until it couldn't, then I backed the screw out one turn and called it good. It high idled well enough cold but could still pull the rpm's down enough when warmed up.

Well, until I went to low elevation, then I had to back the screw out some more from the denser air to pull the idle down further, then wind it back in when I got home (6000 feet elevation change) hence I decided to add an IAC valve.

[Fueler]

Ok, I think I got a grip on it.
Is there a couple of different IAC that people like to use?
I see one on the net that looks like it has an air filter incorporated into it and an AN fitting hookup. Anyone know what that is?