Is an Idle Control Valve really needed?

[turbo4agte]

My question is, is an Idle Control Valve necessary when going with a full standalone?

Im going to be making my own intake manifold, using an aftermarket 75mm Mustang throttle body which has no provisions for an ICV, along with a full Megasquirt standalone. I fully understand how an ICV works... its basically a vacuum leak controlled by a stepper motor, solenoid, or coil that allows for better cold start driveability.

Since the standalone I will be using has full enrichment control based on coolant temperature, couldn't I just tune that? or is a vacuum leak still necessary for something other than emissions?

[BigWorm]

My motor runs ok without an idle up valve, it works fine, just idles a bit low & rough when cold, but perfect once warm (running an autronic SMC).
I would still recommend using one though, they're not hard to hook up (tap a fitting into your manifold & either hook the other end up to your intake pre-throttle body or just have a little air filter on it) and will make cold starting & running a bit nicer. And the MegaSpurt should have enough aux. outputs that you won't have to sacrifice idle control for something more important.
I'm planning on fitting one to mine soon, just to make it a bit more pleasant to drive when cold & improve the cold idle.
If you're building a dedicated track car it's probable less necessary, but still desirable.

[turbo4agte]

My car will be a mainly street driven car and likely have A/C. How would that setup work if I needed an idle up for the A/C?

[BigWorm]

Then it's a very good idea.
I'm not sure how the megasquirt in particular controls idle, nor any other aftermarket ECUs for that matter (someone here will know...) but I imagine on some/most ECUs it'd be a closed loop system, so the ECU could maintain a minimum idle, whether it's caused by extra load from engine accesories or cold running.
Otherwise I guess it'd work off engine temp & need a signal from the A/C when it's on to work, which would be easy if the ECU was controlling the A/C.
It may also come down to the type of idle up valve....

Keen to know myself.

[Mos]

Currently I don't have and idle up valve. Makes cold starts more difficult and sometimes it won't idle while dead cold - though none of the cold start stuff has been tuned yet. It copes with the A/C at idle once warm.
I wouldn't rely on fuel and ignition only as forms of idle control as there will be situations, however rare, where that alone will not be enough (eg. hotel valet ) - I don't know if properly tuned cold idle would alleviate all or some of the problems but it's more of a workaround than a proper solution imho.

A/C idle up in older cars (ie 4A-GE times) was independent of the ECU - just a solenoid activated by the same wire as compressor clutch. Newer engines (1JZ-GTE, etc) control the A/C output and idle speed accordingly, pre-empting a/c turn up by lifting the idle slightly before engaging the compressor.

The most common valve was the ford whatever 2 wire PWM as it was easy to control with one ECU output, having a decent range range. You can't get it new in Aus anymore - not sure what the situation is in the US or whether they were ever available there.

Mos.

[ed]

my engine (ITB's and big cams) was undrivable without an ICV. now it has one, its function is so simple, and works great

[thechuckster]

Being Florida based, you'll probably have (at wrecking yards) a wider range of ISCV's to choose from.

If the car was a weekend toy then you could probably get away with it, but a daily driver with AC really needs an idle-up for cold starts and A/C idle control (if you are stuck in traffic).

To get a sensible cold idle (with warm-up enrichment and throttle cracked open a bit) would result in a way too fast idle when the motor is warm.

If you want something simple, find a largish VSV (e.g. on-off) that you can run via a relay from MS without needing a FET or higher-rated transistor on the fast idle output pin. With a diode or two, you should be able to get the ECU and A/C switch to drive the same relay.

Bigworm: megasquirt does all kinds of idle control - but you have to add hardware to suit (driver circuits) and if it's PWM based, tune the PWM control. It can also do closed loop control for PWM and stepper-motor devices.

[oldcorollas]

one or a couple of normal "AC idle up valves" (is that VSV?) would work. it just analog and only for cold starts or when AC turns on, but better than nothing and easy to control.

if you want to actulyl control the idle speed when warm, rather than just cracked throttle, then PWM ISCV is good.

the "vac leak" is so more air gets into motor, as you need slightly more power to idle when cold, than when warm (aiui). the mixture will still be relatively rich, but the air is for more power

edit: ie, the ECU controls emissions by how much fuel goes in, but the ISCV controls how much power the engine makes at idle, same as using your foot.

[wilbo666]

one or a couple of normal "AC idle up valves" (is that VSV?) would work. it just analog and only for cold starts or when AC turns on, but better than nothing and easy to control.

As a note I think of 5me's the AC idle up solenoid was adjustable....

Personally I'd be looking to use a PWM style IACV as suggested.

Cheers
Wilbo

[jeffro ra28]

Please excuse my ingnorance. what is PWM?

[big_zop]

Its an electrical term - pulse width modulation.

Pulse-width modulation (PWM) of a signal or power source involves the modulation of its duty cycle, to either convey information over a communications channel or control the amount of power sent to a load.

In essence - take a square wave with a common frequency. Like a sinusoid wave, half of is above and half is below the origin (ie. average of a mulitple of a single time period will be zero).

Now, instead of a curve, its square and the same prinsiple applies - but the average is used to control something (this case the ICV). If its equal above and below, its considered 50%, if its all the minimum, then 0%, if its all the maxiumum, then its 100% and can be varied completely from 0-100 to give a very wide range of control.

Clicky

[Norbie]

Another vote for using some form of idle control. My 2JZ currently has none and it freaking sucks when the engine is cold. Yes you can get away without it, but if you have a standalone capable of controlling a PWM idle control valve, do yourself a favour and hook it up.

[oldeskewltoy]

Hmmmmm, in my current build.... I'm sticking with the idle circuit from the smallport manifold..... The ECU (now MAP) will read the sensors, and supply enough fuel so the original warm up reg and simple idle air bypass will still control the idle.

Now this set up still requires use of a 4AG manifold with idle circuit intact. Fortunately I have a rwd smallport intake to fit the bill

[turbo4agte]

I think Im just going to go with a simple FIdle valve, because I have no plans to run any type of throttle body with coolant lines. Im probably going to use just a simple on or off type of solenoid that I can wire in parallel to the AC clutch coil. Megasquirt can control these types pretty easily and it will be better than nothing and not too bulky.

This way I wont have to worry about hard starts or stalling with the AC on. Thanks everyone for all the advice.

[Stefan]

If your ecu can use PWM aux outs, then do yourself a favour and hook up an idle control valve or stepper motor. Some stock ones require a funny boss to attach to manifold (stock 1G for example is huge), but if you hunt around some just require a vacuum hose - easy. Also, you don't necessarily need a 4 or 6 wire stepper motor if that would use up to many auxs - you can get 2 wire idle valves that apparently work ok.

My setup currently doesn't have one, the cold idle is lopey, needs a bit of accel when totally cold, and to start you need to open the throttle to let extra air in. It works, just isn't as nice as it could be. Haven't got around to installing one but when I was last looking around, there were stock Borsh 2-wire valves that used vacuum tubing rather than a fancy boss.

EDIT: I considered going the simple valve option outlined previously, but if your ecu can do simple PWM open loop idle control then this is actually a much easier option IMO.