Confused on Idle Air Control Solenoids

BlackHat · Post by **BlackHat** » Fri Jul 14, 2006 6:04 am

I've been taking my time putting together my MS1 and trying to research everything out before I run into problems. I have read that the MS1 can control a Fast Idle Solenoid.

Well, I have a 1989 Nissan 240sx w/ KA24E engine. I got into researching the Fast Idle Control Device (FICD is what Nissan calls it) and came to a realization that I also have a Auxilary Air Control (AAC). Here's a link to the info I currently have on it http://forums.nicoclub.com/zerothread?id=185492

There are two connectors, one for the FICD and one for the AAC. Both of these get air from the Throttle body and I think there's another connector there that may be for the Idle-Air Valve... I'm still researching that one though.

The air regulator, curiously enough, also has a solenoid. That confused me too, because I was under the impression that Air Regulators just used heat from the engine to determine when to cut off. I guess Nissan also let the ECU control that.

Finally, the question I'm wondering about is, how much of this can the MS1 control? Also, if anyone has tackled anything like this before I would greatly appreciate the help.

(All of the devices just mentioned are solenoids, except maybe the Idle-Air Valve in the throttle body. I'm not sure about much on that one yet.)

Post by **jsmcortina** » Fri Jul 14, 2006 6:45 am

How many wires on each valve?

The AAC sounds like a "normal" 2 wire idle-solenoid which can be controlled by MS1/Extra on the MS1 chip. See http://megasquirt.sourceforge.net/extra and PWM idle.

The FICD nobody appears to know about. Try without it.

On an EFI can you can get away without the idle valve by opening the throttle some more, but the idle valve makes for more pleasant cold running as the idle starts high and reduces as the engine warms up.

James

BlackHat · Post by **BlackHat** » Fri Jul 14, 2006 6:53 am

FICD according to the factory service manual is listed as the device that allows for higher idle when the A/C is turned on. The only problem is that it's been tested when the A/C is removed the FICD is still needed (idle problems when it's removed/disconnected). Of course, I have no clue how it would work connected to an MSEFI

Post by **jsmcortina** » Fri Jul 14, 2006 6:57 am

The way Megasquirt functions - speed density method - using a MAP sensor, you can compensate for no idle valve by opening the throttle, either on a screw or with your foot.

Don't let the idle valves hold you up.

I ran my car with no idle valve for a few months before I decided to fit one, it worked.

James

BlackHat · Post by **BlackHat** » Fri Jul 14, 2006 7:06 am

I'll probably just try with the AAC valve and see how it goes. The A/C is going to stay in the car running off the stock ECU. I wouldn't think it (the stock ECU) could control the FICD unless it was still getting engine info from other sensors, so I'll just leave it unconnected... or maybe figure out how to remove it completely and just let the MSEFI handle everything. (except A/C that is)

Thanks a bunch for the input!

BlackHat · Post by **BlackHat** » Mon Jul 24, 2006 7:22 am

I didn't want to make a new post as this question is just an extension of what I've already asked here.

I've been looking at the setup some more and came to the conclusion I need some clarification on the impact of some of these devices. The air regulator as I mentioned before has a connector (2 pin). Is this a common occurance? Also, would an Air regulator be enough for idle controls alone, or do I also need to have my AAC? Finally, would the air regulator be controllable by MSEFI or do I need to find one that is mechanical and works by engine temp alone?

I'm still researching some of the AAC/FICD functions to see what I can do there, but is it possible to replace that assembly with a generic FIDLE valve that would work with MSnS? I'm pretty sure the fabrication on my KA24E would be easy for any generic valve.

Also, as a side question. Can MSEFI make up for drops/increases in RPM due to A/C turning on/off?

Thanks for your time!

RNash · Post by **RNash** » Mon Jul 24, 2006 2:22 pm

BlackHat
As James said above, speed density method allows you to increase idle speed simply by letting more air into the engine. This can be done by an air valve of some kind, by cracking the throttle, or even a vacuum leak. When the MAP sensor sees more air (less vacuum), MS squirts more fuel and RPM's go up. So a fast idle valve is really just a controlled vacuum leak. Any valve that lets more air in will increase idle. The trick is how much. Big hole = lots of air = more RPM.

What you need to know, (and I can't answer) is are the stock valves just a solenoid that open and closes or are they PWM. PWM turns the valve on and off very quickly so that it can be controlled from wide open to fully closed.

MSnS allows you to use ether solenoid or PWM control to control a valve.
Standard Fidle controls just a on-off solenoid. PWM controls a special type of valve that is designed to be variable. PWM can be set "open loop" to run a fixed idle speed until that engine reaches a set temp. Or it can be set "closed loop" to try to maintain a set idle speed under different loads such as A/C.

It is possible to use a PWM valve such as a 2 wire Ford to control your idle and automatically compensate for different loads.

See - http://megasquirt.sourceforge.net/extra/pwmidle.html

And - http://www.msefi.com/forums/viewtopic.p ... highlight=

BlackHat · Post by **BlackHat** » Tue Jul 25, 2006 9:05 am

So basically all you need is one valve that can control air flow for open and closed idle air functions? I'm just trying to understand why there's 3 different devices on my engine that control idle air flow. From what I'm reading the MSEFI doesn't need that many, is there some benefit for it I'm not seeing?

I've seen the first link in my research. The second is extremely interesting. As I mentioned, I can create a spot for a generic PWM valve where my Idle controls are now fairly easily. I'm very tempted to do just that. (Thanks tons for that link)

BlackHat · Post by **BlackHat** » Thu Jul 27, 2006 6:56 am

I think I figured it out. Would someone tell me if this sounds right?

A solenoid is either 100% on or 100% off right? Which would mean the only limiting factor in how much flows through the solenoid is the orifice size. This kinda makes sense as to why there's 4 different idle air controls.

The air regulator has a ecu connection on it. That would make sense if the ECU wanted to know when the air regulator was on (letting air in the intake) and when it was closed. The air regulator would basically be the open loop idle control. Once the engine heats up, the regulator is closed and the engine needs another way to get idle air.

The AAC takes care of all of the idle air needed in closed loop. With the exception of when the A/C kicks on. Then the ECU turns on the FICD valve. Does this sound logical? (oh and the 4th idle air control is the idle screw)

The car is a 1989 Nissian 240sx. From what I've been able to gather, PWM valves came out later than that (at least were not used by cars till sometime after that). This is all reasoned out and not known fact by me, so I'm kinda curious if I got it right.

The second part to the puzzle is, if the MSEFI can control the AAC valve and use the signal given by the air regulator (if the MSEFI just went by temp sensors it seems logical the air regulator may not be fully closed, so the only way it could be sure is by recieving a signal from the air reg). I can get the FICD valve to work off of the old ECU (which will be running the A/C controls). Will the MSEFI allow the idle to jump by ~150 rpms when the FICD valve is opened due to the compressor turning on or will MSEFI try to do something weird to regulate the rpm? The way my logic is running I don't see what the MSEFI could do to limit it other than cut back on fuel which wouldn't be a good thing. (again, I'm assuming solenoids can only be 100% open or closed and not be able to do what a PWM does) It would seem the MS is stuck with just leaving the AAC valve open.

Sorry for the lengthy post, I started trying to figure this out and I have a bad habit of being single minded until I figure something out

RNash · Post by **RNash** » Thu Jul 27, 2006 1:30 pm

Could you use the AAC solenoid for warm-up, controled by MS "Fidle" output, use the idle screw to set your normal idle speed and then wire the FICD to the AC compressor (with a relay if needed) to turn on when the A/C kicks on?

BlackHat · Post by **BlackHat** » Thu Jul 27, 2006 1:45 pm

My only concern with that approach would be that the hole for the AAC is smaller than the one for the Air Regulator. It may not be able to push enough air during startup to run at normal open loop warmup rpms.

What other reason does an engine need a idle air control for besides the regular idle screw and open loop startup? I don't really imagine the coolant cooling down while it's running... at least not to the point it'd need to idle high.

RNash · Post by **RNash** » Fri Jul 28, 2006 9:06 am

I did some research for you.
You can find a service manual here
http://www.zeroyon.com/index/content/view/24/47

Look in E_Theory.pfd

The AAC valve appears to be a PWM closed loop used for 'fine tuning' idle speed.
The 'Air Regulator' is a warm-up valve, the wire feeds an electric heater to help heat the valve.
The FIDC valve is a load compensating on/off valve.

You may be able to get by with just the air regulator wired to the fuel pump relay (for warmup), and the FIDC wired to your A/C. Then you could also try to control ACC with PWM if needed.

You will just need to experiment with it and se what works.

BlackHat · Post by **BlackHat** » Fri Jul 28, 2006 12:09 pm

Ok, actually I found out some conclusive information about my setup... I was speculating on some of it and aparantly speculating incorrectly.

The air regulator is heated by the ECU. The connector on it is NOT a sensor, but input for the electricity needed to heat up the air reg. The AAC and FICD valves are both PWM. (Actually, I also found out the AAC is 100-200hz in frequency). The other bummer, is that the FICD valve not only turns on when the A/C kicks on, but also when the AAC valve needs extra air for idling.

I'm thinking along the lines of putting a PWM valve that MSEFI can control where the Air reg is and putting the FICD valve alone on the back plate where it is now (and welding up the hole the AAC uses). That way, MSEFI can control idle during open and close loop with this new PWM and when the A/C turns on it will help load by turning on the FICD valve at the same time (so the MSEFI won't be hit by a sudden strain on the engine).

That logic sound good?

Sorry for the round and around I'm giving on the topic, some of this is thinking out loud. I appreciate how patient you've been with me. What's in this post is verified by other sources. (As far as how my 89 nissan 240sx uses Fast Idling)

Megasquirt Support Forum (MSEXTRA)

Confused on Idle Air Control Solenoids

Confused on Idle Air Control Solenoids

FICD

Idle Valves

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