Go Back   ModernMuscleCars.net
User Name
Register FAQ Members List Calendar Mark Forums Read Home

Welcome to ModernMuscleCars.net.
If this is your first visit, be sure to check out the FAQ. You have to register before you can post. Registration is free! Click the register link above to proceed.
Our Sponsors
Advertise with us! Grundy
Collector car financing
J. J. Best
Collector car financing
Mecum Auctions
Collector car auction house.
Performance Restorations
Car restoration experts.

Electronic Manual Idle Control
by Richard Cowan (a.k.a. RCowan99SSConv )

What Is It?
This system gives the driver the ability to move the iac pintle in and out via electronic signals, independent of the pcm

How Does It Work?
The IAC pintle is activated by a stepper motor.  This system uses a separate stepper motor drive circuit that the driver controls via switches.  Stepper motor Run/Hold, Direction, and Speed are at the touch of a button.  In the final version I have adapted a single DPDT toggle switch which controls run/hold and direction with an established stepping speed.

Why Bother?
If you have installed an aftermarket cam, especially one with a lot of overlap (i.e. 112 LSA Hot Cam) it may idle poorly or not at all at the PCM's desired idle speed.  This is particularly a problem for Automatic cars which tend to idle at about 550 in park and 600 in drive.  This problem is exacerbated by the way the PCM controls the IAC pintle.  If you have ever monitored IAC counts and idle with AutoTAP you have noticed that the PCM is constantly moving the IAC pintle in and out in an effort to maintain its desired idle speed.  You may also have noticed that even idling in park, the engine rpms can vary more than 100 rpm!  This PCM "fidgeting" makes it that much more difficult for the car to keep idling with that "loopy" cam experiencing "idle hunt."

If you don't want to pay $$ for custom programing (and even if you do) you have a couple of options to address this problem.  1)  Raise the idle by forcing your Throttle Body (TB) plate to be slightly open when your foot is off the gas.  The easiest way is to adjust the TB stop screw to keep it slightly open.  Some have gone so far as to forcibly bend the tab to do the same thing!  2) Drilling your TB idle air hole larger to allow more air at idle.

So what's wrong with these methods?
Nothing, really, but the PCM will fight you and you have Zero adjustability.  The TB hole drilling will allow your car to idle at a lower idle speed with less surging, but as you drill out more, the PCM closes the IAC pintle, ultimately to zero, to lower the idle.  The positive side effect to this is that all that variability caused by the IAC bouncing around is reduced significantly.  (This is why it is good to have low IAC counts...the computer is tinkering with less of your air).  The negative is that it takes this source of air away from you.  If you could force the IAC pintle open some you could get away with a smaller TB hole and higher idle without tweaking the TB plate stop.  Also with these methods you have no adjustability.  You have to fix an idle you can live with.  Too much and your car goes idling down the road at 30mph in the middle of winter.  Too little and you are still dealing with the same old problems of idle hunt and dying.  Just-right usually means it will cruise fine, but it has to be babied to get it going.

So why do I want to do this when I can still just drill the hole and tweak the TB stop?
Once you drill the hole and tweak the stop & do the TPS mod to adjust for your adjusted TB stop setting, these are "fixed" unless you take the time to undo the changes.  For a lot of people (like me) the car idles fine..once it warms up!   However, starting up and getting the car out of a parking space and cruising on the road can be an exercise in two-footed driving and frustration.  After your car dies 3 times getting out of the parking lot, and you have pissed off the other people and embarrassed yourself trying to get out, you can see where it might be nice to have the ADJUSTABILITY!  With this mod you can up the idle -- say 1200 ish (or 3000 if you want ;) )-- until you get going and then move it back down to "normal."  For me, I had to feather the gas for about 30 seconds to a minute until it stopped "hunting."  Then I would have to carefully and slowly back out of the parking space, hold the gas down a bit when shifting from Reverse to Drive (thank goodness for loose Torque Converters) and get going.  With this mod, at the SAME idle speed (850 per my PCM) ... I have to hold the gas in about 10-15 secs and then the idle is rock solid!  I can then back out and shift to Drive without fear of stalling and dying.  For a cold start I have to bump the idle higher... maybe 1100rpm.  Then after I am moving on the road I bump it back down to 850-900 or so.  Its that ADJUSTABILITY that is the best advantage.

The second BIG advantage is the IAC Pintle is now steady.  Even at the same idle rpm, the car idles more smoothly than it did before--just because the IAC Pintle is still.  Idle hunt went from 500-1200 swings (for 30secs to a minute)  to 800-1000 swings (for 10-15 secs).  By using the IAC Pintle to bump my idle up 50 rpm or so, it doesn't hunt at all anymore!  (This is with hotcam and .250 TB hole drilled out).  Monitoring the Idle speed with AutoTAP shows an average variability of about 50rpm now compared to over 100rpm like before!  That's the secret to calming idle hunt with this mod.

OK, OK, Enough already! Show me the mod!


If you read/use any of the information on this page, you do so at your own risk.  This work was performed on a 1999 Camaro SS.  Your IAC may vary.  This modification will give you the power to make your car die at any moment.  It will also give you the power to run up the idle to 3000 (wide open IAC).  Both cases are potentially dangerous and you take this responsibility upon yourself when you choose to do this modification.  Improper handling of your IAC can permanently damage it.  (No gorilla pintle-pushing, please).  Improper wiring can cause your IAC to malfunction (i.e. it could run up to 3000 all by itself if you don't do it right).

There really isn't a lot to it.  I determined the voltage and current requirements of the IAC stepper motor.  I located a Stepper Motor Driver kit from an electronics manufacturer.  I confirmed that the kit could handle the stepper requirements.  I also made sure it had all the necessary functions (direction, run/hold, stepping speed adjustability).  The kit I found had the added benefit of being able to conveniently "piggy back" the switches on the printed circuit board with remote switches--just run wires to the box.  This also allowed me to condense the controls to a single DPDT (double pole, double throw) toggle switch.  I soldered the kit together.  I cut the IAC wires and removed the unit from the car.  I connected the IAC to the board and connected a power source.  It worked :).  I then installed it on the car and added the remote toggle control.

I would first of all like to acknowledge Steve Harmon (aka "just me") who inspired me with his Manual Idle Control mod and made me realize how nice it was to have the ADJUSTABILITY that these mods offer.  Also a "Thank you" to the other guys at Tech-LS1.com for their advice and encouragement.

Here's how it all happened and how to do it yourself, if you wish.

Step One:  Determining Stepper Motor Requirements
The first thing to do was to find out what voltages and currents my stepper motor was getting.  The picture  below shows us measuring voltage across a coil.  We stabbed pins through the green/white and green/black wires and measured the voltage across them.  The motor steps quickly, but it was obvious that it was swinging between +10Volts, 0volts and -10 Volts.  The currents through the coils peaked at about 180 milliamps.  The motor appeared to be a bipolar type due to the constantly changing polarity across the coils and the fact that there are only 4 wires.

I won't go into the basics of stepper motors, but if you search on the web you will find a ton of info on these relatively simple devices.

Step Two:  Obtain Stepper Motor Driver
Searching the web, I found a stepper motor driver kit at Ramsey Electronics.  This kit handles steppers from 5-15VDC, bipolar or unipolar steppers, and had the controls I was looking for.  Conveniently, the power input requirement is 12VDC.  The Assembly manual for this kit can be read on Ramsey's web site.  The kit is SMD-1.  Cost was $24.95 with an optional case for $14.95.  I bought both.  You can see the final product in the picture below:  You could make your own case, especially if you are going to hide it and use the remote toggle switch (recommended) described later.  Their case is very clean and looks decent.

Step Three:  Putting It All Together
When I got the kit, I soldered all the components on the printed circuit board.  The manual is very easy to follow and is written so that people with little or no electronics experience could build it.  It took less than 1.5 hours to assemble.  Here you can see the completed printed circuit board with the two parts of the DC power plug in the upper right.

Step Four:  See If It Works :)
The next thing to do is find out if its going to work.  I checked every connection over a few times to make sure the connections were complete and clean, and to make sure I didn't create any solder "bridges"--when  two things are electrically connected that shouldn't be.  I had obtained a 2.5mm DC power plug from Radio Shack and I now soldered two wires to it to make my power connection.  You can see it in the figure below.  Yellow is hot, Black is ground.  Hot is the inner surface, ground is the outer surface.  The black piece slides up and screws onto the metal plug.

I connected the other ends of the cut wires to a Voltage generator (a 12V DC battery works fine).  I plugged in the power and pushed the power switch on the kit to "On".  The first good sign is that nothing smelled, or smoked, or was burning.  I turned it off and disconnected power.  Then I cut the four wires to the IAC on the car, removed the two screws, and brought the unit inside.  I pushed the four wires into the six-pin connector on the back of the kit's board.  There are four ways to put them in and all are "correct."  Pins 1 & 2 are for one coil.  Pins 3 & 4 are for the other.  So you put either both blue wires in 1&2 or both in 3&4.  Once you do that, make note of where the one with the black strip is.  If you put blue wires in 1&2 and the black striped one  is in 2, then you put green wires in 3&4 with the black striped green one in 4.  Likewise, if you put the black striped blue wire in 1, then the black striped green wire goes in 3.  This describes two ways to wire it up.  The other two are the same if you switch the blue & green colors as described above.   The only difference is the directions are reversed.
    So I pushed those four wires in the back correctly and turned on the power.  The direction button was set to CCW.  I pushed the Run/Hold button and the motor started stepping!  You can hear it step, you can see it move, and if you put your finger on it, you can feel it pulsing.  I experimented with adjusting the potentiometer which controls the stepping speed.  I wanted to get it slow enough to count the steps while it moved a certain distance (so I could estimate step size) but I couldn't get it slow enough.  I changed directions on the fly and made it stop and start.  It worked great!

Notice the one button is labeled "Run/Hold" and not "Run/Stop."  The difference is critical.  "Stop" implies cutting power to the stepper.  With a stepper motor, if you want it to hold its position and it is holding back something (like air rushing past it) you have to keep a charge on at least one coil after stepping stops.  This charge will hold the motor fixed.  In a stepper its the force of the magnetic field that turns it.  This force also holds it.  Without this holding force, the air will push the IAC open all the way and your car will idle at about 3000rpm.
    I experimented with the limits of the pintle also.  The figure above shows the pintle all the way into the housing (max air flow).  If you get it all the way in like this it will just wiggle there, doing no apparent damage.  The figure below shows it stepped all the way out... a little too far  :).

When the pintle came this far out, I just reversed the stepper and it screwed back in place.  If yours happens to fall off on the table you can screw it back on by hand (according to Helms manual!).

I measured the stepper currents and voltages with the stepper being driven by the kit.  The currents were virtually the same but the voltages were a bit lower... around 7 volts.  The SMD-1 manual advises you check the current because the Integrated Circuits' max allowable current is 500mA.  Our ~180mA was fine.

So It worked on the kitchen table.  Would it work in the car?  I used the kit to move the pintle to the approximate position it had when I took it out and disconnected everything.

Step Five:  Install It In The Car:
I ran four wires from the IAC through the firewall to the interior of the car.  I already had a hole and fitting on the driver side that I used for my line lock and gauge senders, so I used the same one for these wires.  In the picture below you can see it looks stock and only the trained eye would see that the IAC wires are in a different convoluted tubing that goes somewhere else :).  I tucked the ends of the stock IAC wires inside the stock convoluted tubing and put the "free end" of the stock convoluted tubing over those taped wires going to the throttle position sensor.

I got power from a switched 12V source under the dash.  I also used a ground wire there for the kit's ground.  I plugged it in and connected the stepper motor wires from the IAC.  I pushed the power button on the kit.  I started the car.  It started at about 1200 based on where I had left the pintle.  The direction button was on CCW and I pushed Run/Hold to start it stepping.  The idle slowly began to rise to 2000.  I pushed Run/Hold again and it held there.  I then pushed the direction button in (CW).  I pushed Run/Hold to run and the idle started coming down. :)  I held it at about 900.  Below you can see the box in the car.  Does your passenger seat often look like this?  ;)

"Tuning Aint Easy"

The idle was nice and steady.  Later AutoTAP would show it varies over a range of 50rpm or so.  With the PCM jiggling the IAC pintle all around that value was over 100rpm.

So it works!  But ya know, that box is kind of an eyesore and trying to manipulate all those buttons while you are riding around is a pain.

Step Six:  Remote Toggle Switch:
I consulted the manual which shows you can adapt remote switches to control everything.  The DPDT switches in the kit all have "solder lugs" on top which make them really easy to "piggy-back".  It was my goal to use a single DPDT toggle switch to control Direction and Run/Hold.  I would hide the box somewhere and just use this switch.  I would leave the power button on because the unit does not get power until you turn the car on anyway.  Plus you want it to come on right when you start the car so it will hold the IAC in place as you startup.  Also I toyed with the stepping speed dial, got it where I wanted and decided I would leave that set and not worry about remote control of stepping speed.  I obtained a DPDT Momentary Toggle Switch from Radio Shack and installed it.

The way it works is when you push the switch to "side 1" it causes the kit to switch from "Hold" to "Run" and run in a CW direction.  Push the switch to "side 2" and it causes the kit to switch from "Hold" to "Run" and run in a CCW direction.  Release the momentary switch and it snaps back to center and holds the stepper in place.  Basically, push the switch one way, the idle goes up.  Push it the other way and the idle goes down.  Take your finger off and it holds.  I was really pleased how this worked.  I have temporarily stowed the Box behind the center console and run the toggle switch up through the ash tray.  Here you can see in this driver side view, I have tucked the box away and put the switch in the ashtray, unmounted for now.  The cable going across the picture is for AutoTAP.

That's It!
If you ever want to go back to stock, all you have to do is disconnect your stepper driver wires and reconnect the stock wires.  That would probably take you less than 10 minutes.

If you use this controller to keep your idle more than 200 rpm above or below the PCM's desired idle speed, you will get an SES light and set a code for idle being higher/lower than expected.  This is one of those non-codes that doesn't do anything but annoy.

A Point For Improvement
Some indication of actual IAC Position would be helpful.  Before, we had IAC counts.  Now we don't have anything but watching how the engine responds to changes.  To make it more difficult, there is a lag between when you open up the IAC and when the motor responds.  You move the IAC and then it takes about a second for the motor to respond.  It should be possible to add something like a pair of seven segment displays and a counter to count every step, or every fourth step for example.  Then you could measure relative differences in IAC position every time you change it.  For example, suppose you always open it up to give ~1100 rpm idle during starting, then when it gets warm you step it down to ~900 rpm.  If you always turn the car off at this 900 value, then when you turn it on perhaps the counter is at zero.  Then when you move up to your 1100, the counter steps up to.. 50 for example.  You then know exactly how far to step it down when you get moving.  Just step down until the counter is back to zero.  You would always have more consistent idle speeds this way.

Good Luck and let me know if this mod works for you!

Let's Ride!

by Richard Cowan

All times are GMT -5. The time now is 09:05 AM.

Powered by: vBulletin Version 3.0.5
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Copyright ModernMuscleCars.net