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Stepper Idle Valve Control

     UPDATED: September 5, 2018                       CONTACT       
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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. 
Some refinement would be a welcomed addition.

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.
Valve Specs:
12 volt DC.
Normally closed. Applying power opens valve.
1/2 inch (0.500") hose barb inlet/outlet.
3/8 inch (0.375") inner orifice I.D.
Stainless steel internal parts.
Maximum operating temperature 175 º F.
Made for pressurized water or air.
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 intake manifold. 
<<< 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.

Stepper Motor Idle Air Valve Control

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.

Volvos use a Bosch idle air valve that has either 2 or 3 wires.  To my knowledge these are PWM controlled.  A 4-wire stepper motor, such as that shown here, is different from PWM. A stepper uses two coils with two wires going to each coil to control the stepper motor movement.  I have no idea how a PWM Bosch valve works or if a similar method could be used for one of those. Maybe someone can enlighten me if so.

So this page will specifically go over my project of
Creating a MANUALLY ADJUSTABLE idle speed circuit
using a GM type IAC valve similar to what was done in the above video.
(except without the toggle switch and relay to switch between Auto and Manual).
<<< This is an idle motor from approximately 2000s GM car or truck . There are a few different styles out there, but this is the style I chose.  It 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 to screw in instead of the above motor, which bolts on.
As you will see, I am eliminating a few components from the design shown in the above video. My intent was to create a strictly stand-alone setup that can manually adjust the idle up or down from the dash.  I'm not re-inventing anything.  I'm just using the ideas offered by Jon Lamb in his video. 
Circuits like this are a new thing for me. So please don't mistake me for some kind of electronics wizard.  I'm not, but I'm learning.

You may have noticed that the above GM IAC motor is not really a valve. It's just a stepper motor and plunger. So I started searching for an adapter that I could make, buy or modify to make it into a stand-alone idle air valve
<<< There are a few out there and most are very expensive. I chose this adapter from Accufab Racing.  It was more than I wanted to pay, but it works. It's designed to allow the use of the same GM IAC motor. This adapter is designed for using a GM IAC motor 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.

Assembling Circuit Parts

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 have an existing GM ECU that would be used for the 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 his hand-drawn diagram, so as I worked out what all these components were, I decided to create a new, more detailed diagram below showing each component that went into this project.  This helped me to better visualize the task.  It should help you understand it better too.

C L I C K   T O   E N L A R G E   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 it all up on an electronics 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.

GM IAC Stepper Test
Here's a short video demonstration of the stand-alone Idle Speed Control Circuit.

<<< Here's the mini rocker switch I used for the idle increase/decrease adjustment.  It's mounted in a dash switch blank for my 240.
<<< The mini rocker switch had .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 from top to bottom: 12V OUTPUT, 12V INPUT in the middle, and 12V OUTPUT at the bottom.
<<< Right side view.  Switch pinouts from top to bottom: Output to DIR (Direction) on DRV8825 Driver Board. GROUND is on the middle tab.  Bottom tab is unused.
<<< I decided not to solder everything together like Jon did in his video. I bought a JST mini pin connector kit (see parts list).  It has 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 this stage, things suddenly didn't work.  I discovered that the 5V regulator was no longer working.  Maybe I shorted it. I replaced the regulator and it all worked perfectly again.  Good thing I bought two.

Next is installing all this in the car.
<<< I mounted the new IAC valve under the intake manifold here.
<<< More close up view.
<<< Here's the adjustment rocker switch. It's set up to adjust the idle #1 circuit. Idle #2 is an extra circuit.
After trying the new IAC setup using the two small Ehcotech valves shown at the top of this page, I found the valve the was connected to the new IAC circuit was not allowing enough airflow during cold idle with the AC on.  I decided that the 3/8 inch inner diameter of that valve was probably creating a bottleneck.  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 cold idle conditions.  I found this valve on eBay for about $25.

Valve Specs:
12 volt DC.
Normally closed. Applying power opens valve.
3/4 NPT female thread inlet/outlet.
3/4 inch (0.750") inner orifice I.D.
Stainless steel internal parts.
Maximum operating temperature 175 º F.
Made for pressurized water or air.

If you have any comments or questions, please feel free to email.

All can be found on eBay or Amazon

IAC motor for GM (2007 Chevy Silverado and many others).  4-pole connection.  Cost will be $10 to $90, so shop around.
Connector plug with pigtail for above. Cost is about $10.00.

DRV8825 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.

NE555 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 $15.00.
  LM2940 5.0 volt regulator to reduce voltage to the Generator Board. Cost may be around $2.00.

DPDT (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.

10k Ohm Carbon Film Resistor. 0.25 Watt. TWO NEEDED.  Cost is small.

100 Ohm Carbon Film Resistor.  0.25 Watt.  Cost is small.

100nf (0.1uf) Ceramic Disc Capacitor. THREE NEEDED. Cost is small.

100uf 25 Volt Radial Electrolytic Capacitor. Cost is small.

3 amp fuse and fuse holder for 12V input to the rocker switch. 

Hammond 1591BSBK ABS Project Box Black.  4.4 x 2.4 x 1.1 inches (112mm x 62mm x 27mm).  $5.00.

QLOUNI 2.54mm Pitch JST Pin Housing Connector Kit.  About $9.00.
Not required. You can solder things also. 

IWISS Micro Open Barrel Crimping Tool for JST Terminals.  $17.00.
Not required. You can solder things also. 

Ehcotech 12 volt electric valve, normally closed, 1/2 inch hose barbs, 3/8 inch inner diameter. Under $10.00.

Ehcotech 12 volt electric valve, normally closed, 3/4 inch NPT female, 3/4 inch inner diameter. About $25.00.

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