|Stepper Idle Valve Control
|UPDATED: February 13, 2019 CONTACT|
M A I N S
This page details work on my idle air control functions for my 242 Turbo.
This car uses a programmable fuel injection system from SDS (Simple Digital Systems). I began using SDS almost 20 years ago. Megasquirt is a popular engine management these days, but it didn't exist when I started using SDS, so I have stayed with it.
SDS was originally designed for racing and it does not have a modern computerized idle control function to control a precise stepper type idle valve, like Megssquirt or Microsquirt does. What SDS offers is the ability to trigger a simple electric air valve to enhance the idle for cold warm up or AC idle increase. A simple ON/OFF idle valve is crude and sometimes doesn't work as well as you like.
So this is adding some refinement to my idle functions. A welcomed addition.
For those of you using a GM stepper IAC (factory EMS, aftermarket EMS, Megasquirt, etc.), this extra control may be a welcomed addition for you too. Watch Jon Lamb's video. The ability to switch between normal and custom idle settings from the dash sounds like a pretty cool thing to me.
Your feedback or comments are welcome: CONTACT
|Most Recent Idle Air Control Method in my 242|
<<< This is
an Ehcotech 12 volt
electric valve. I have been using two of these for 10 years with great results.
Both use manual fast
idle switches on my dash for cold starts, etc.
One is also controlled by the AC compressor 'ON' circuit for AC idle
increase. Both are also controlled by microswitches on the
throttle spool that override and shut the valves when
throttle is increased above idle. So the way I have
them set up, these valves are only active at idle.
These valves are found on eBay for under $10 each.
|I use 1/2 inch I.D. silicone
hose for the air lines from the intake tube
(pre-throttle body) to the above valve and then to the
<<< Tuning the airflow in the hoses can be done simply with a hose line pinch clamp like this one pictured. It squeezes the hose and small precise adjustments can be made if needed.
In 2018 I discovered the below Youtube video made by Jon Lamb (comeinhandynow) in the U.K.. It details making your own stepper motor idle speed circuit that can be adjusted from the dash. Jon outlines the manual adjustment method for a 4-wire idle air control valve, such as one found in a GM car like his. It sounded like a fun project.
So the above setup allows a user to manually adjust the idle speed on the fly. This becomes useful if whatever system you're using isn't perfect in every regard. Maybe you want a higher idle during warm-ups or when the AC is on (combined with warm-ups). Being able to do an easy quick adjustment in my 242 Turbo would be a nice benefit.
This is an idle motor from approximately 2003 and later GM
cars or trucks . There are a couple different styles of
idle motors out there. The one I picked uses the
4-wire connector plug shown here.
This is an earlier style GM idle motor that came in cars
until approximately 2003. It will also work, but you
will need to mount it differently since it's made with
threads to screw into a manifold instead of the above
motor, which simply bolts on. And this type uses a
different 4-pole plug.
|You may have noticed that the above GM IAC
motor is not really a complete valve. It's just a
stepper motor and plunger. I could not find a 4-wire
idle valve with integrated IN and OUT hose barbs for air
hoses. Maybe one exists out there, but I found nothing
that I thought would work for me.
So I started searching for an adapter housing that I could make, buy or modify to make it into a stand-alone idle air valve.
There are a few housings like this out there and most are
very expensive. I chose this adapter from Accufab Racing.
It was more money than I wanted to pay, but it works. It's
designed to allow the use of the same GM IAC motor I chose.
This adapter was originally designed for adapting a GM IAC
stepper motor for use on a Ford engine.
<<< Here's a bottom view.
Here's a view inside. This hole starts at about
.875 inch diameter. That first step is about .250 inch
deep and it reduces to about .750 inch. The .750
inch hole depth is about 1.1 inch and the final size is
beyond that is 7/16 inch (.4375 inch).
If you're handy and have the machine tools or drills, making one of these would not be very difficult either out of aluminum or maybe even a sturdy plastic block.
Coincidentally, those IN and OUT holes on the bottom were
7/16 inch diameter, which
is the correct size for a 1/4 inch NPT thread tap.
After taping the threads, I inserted 1/4 inch NPT
nylon hose barbs (for 1/2 inch I.D. hose). Now I have a stand-alone IAC
valve. I guess I'm committed now. Now it's time
for the circuits.
I was concerned that the .375 inch I.D. of those hose barbs might be too small for the airflow needed. If this became the case, then I could optionally drill the holes to 37/64 inch for 3/8 NPT thread. So far I have not made any changes.
Jon Lamb's video has a diagram showing all of the components he used to complete his project. He will also email you a PDF document showing more detail if you like. Check his video description for that.
My version uses a few less parts, since I don't already have an existing GM ECU or an EMS that uses this type motor for primary idle control. So I don't need the relay or the toggle switch Jon used to switch from Auto to Manual.
I had a little trouble interpreting and following Jon's hand-drawn diagram, so as I worked out how these all these components went together, I decided to create a new, cleaner diagram below showing each component that went into my project. This diagram below is a little different from Jon's diagram. It doesn't include the relay Jon used to switch between his factory EMS and manual idle control, since I'm not using that relay. This helped me to better visualize the task. It should help you understand it better too.
If you need help with this diagram or with the one using the relay, contact me.
C L I C K T O E N L A R G E B E L O W I M A G E
A printable PDF version of this diagram is available: CLICK HERE (1.2 mb)
Before actually building this thing, I hooked up the raw
circuits on a solderless breadboard to make sure I had it
right. It worked as promised. If you check out
the below video, you'll get to see my test in action.
Here's the mini rocker switch I used for the idle
increase/decrease adjustment. It's mounted in a
dash switch blank panel for my 240.
mini rocker switch has .187 inch tabs on the back. I had
some uninsulated female .187 inch terminals, so I
covered them with heat shrink tubing. Here's a view from the left
side. Switch pinouts on this side from
top to bottom are: 12V OUTPUT (top), 12V INPUT (middle),
and 12V OUTPUT (bottom).
|<<< Right side view. Switch
from top to bottom are: Output to DIR (Direction) on
DRV8825 Driver Board (top). GROUND (middle).
Bottom tab is unused.
decided not to solder everything together like Jon did
in his video. This is a personal preference thing.
You might like soldering stuff. I don't
particularly care for it. Solder joints are prone
to cracking and when that happens, you'll have a hard
time finding the problem.
I bought a JST mini pin connector kit (see parts list below). It worked out nicely. This connector will connect the box (in the dash) with four wires going through the firewall to the engine bay for the IAC valve.
Here's the project box I stuffed everything into. When
testing again at a final stage, things suddenly didn't
work. I discovered that the 5V regulator was no longer
working. Maybe I shorted it when moving
stuff around. I replaced the regulator and it all worked
perfectly again. Good thing I bought two of them.
Next step was installing all this in the car.
mounted the new IAC valve under the intake manifold
close up view.
Here's the adjustment rocker switch. It's set up to
adjust the fast idle #1 circuit. Idle #2 is an extra
circuit that can be used during warm-ups.
|After trying the new IAC
setup using the two small Ehcotech valves shown at the
top of this page, I found the valve that was connected
to the new IAC circuit was not allowing quite enough
airflow during cold idle with the AC on. I decided
that the 3/8 inch
inner diameter of that valve was probably not
big enough. So I bought this valve pictured. It's
a larger valve, also with a plastic body, with an inner diameter of 3/4
inch. It solved the problem and now the
engine gets plenty of airflow in any cold idle
condition. I found this valve on eBay for about
|If you have
any comments or questions, please feel free to
motor for GM (2007 Chevy Silverado and many others).
4-pole connection. Cost will be $10 to $90, so shop
|Connector plug with pigtail for above. Cost is
Stepper Motor Driver Board or Module. Size is typically
less than an inch long. Typical input may be 5-45 volts.
Cost may be about $2.00 to $4.00.
Pulse Module Square Wave Signal Generator Board with LED
Indicator. The LED is
needed for this project. There are a lot of these boards
without an LED. Get one with it. Size is
typically about an inch or so wide. Typical input will be
5-15 volts. There are three required connections:
VCC, GROUND and OUT. Cost may be around $5.00 to
5.0 volt regulator to reduce voltage to the Generator
Board. Cost may be around $2.00.
(Double Pole, Double Throw) mini rocker switch, 6-poles on
the back. Momentary (ON), OFF, (ON) function. Front
size is about 1/2 x 1 inch. Cost is about $5.00.
Carbon Film Resistor. 0.25 Watt. TWO NEEDED. Cost
Carbon Film Resistor. 0.25 Watt. Cost is
(0.1uf) Ceramic Disc Capacitor. THREE NEEDED. Cost is small.
|100uf 25 Volt Radial Electrolytic Capacitor. Cost is small.|
fuse and fuse holder for 12V input to the rocker
1591BSBK ABS Project Box Black. 4.4 x 2.4 x 1.1 inches (112mm x 62mm
x 27mm). $5.00.
2.54mm Pitch JST Pin Housing Connector Kit. About
Not required. You can solder things also.
Micro Open Barrel Crimping Tool for JST Terminals.
Not required. You can solder things also.
12 volt electric valve, normally closed, 1/2 inch hose
barbs, 3/8 inch inner diameter. Under $10.00.
12 volt electric valve, normally closed, 3/4 inch NPT
female, 3/4 inch inner diameter. About $25.00.
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