This IAC stepper controller is designed to control a typical 4 wire IAC Stepper Motor from a ground

switching PWM signal from your ECU.


It has been tested with GM , Marelli and Renault type 4 wire stepper motors but should work with virtually any standard automotive 4 wire idle stepper motor.


This PWM2Stepper module has been designed by ourselves and built in the UK by a professional electronics assembly company.
You can only buy this module from ourselves or our selected partners.

 

Contents

1 x PWM2Stepper Control Module
1 x Molex IP67 Connector
7 x Molex connector terminals


Operation

This module converts the ECU PWM 0% to 100% signal into steps for the IAC
It will control the stepper from fully closed at 0 steps to open at 200 steps.
Whilst many steppers will go to around 240 steps maximum at around 200 steps they are effectively fully open in terms of air flow.
We choose this 0 to 200 range of operation to keep the calculations easy.

Typically 1% PWM change equates to 2 steps change so,
10% PWM = around 20 steps
50% PWM = around 100 steps
100% PWM = around 200 steps

Unlike other converters this module is not “ Always ON “ so does not overheat the module or the stepper motor when the stepper is stationary.
After a few seconds of no movement commands it goes into a sleep mode shutting off the stepper power and then reawakens when it next receives a move command.

 

Physical Specifications

Waterproof assembly designed for engine compartment mounting.
Complete with IP67 waterproof Molex connector for plug in connection
Generation 2 units now have included mounting flanges
Dimensions = Approx 75mm x 75mm x 27mm ( including mounting flanges and connector )

 

 

Technical Specifications
 

Operating Temperature

Ambient temperature of engine bay should not be more than 60 degrees C
( Protect from higher temperatures using shielding or relocation of module )

 

Operating Voltage

Minimum normal working voltage = 9 volts
Maximum normal working voltage = 15 volts
Short term Spike voltage = 20 volts

If the voltage drops below 9 volts the stepper motor may become lost and not open fully.
If this happens, for example during cranking with a very discharged battery, it will reset itself during the next ignition key cycle from OFF to ON

New for Generation 2 Units

We have now programmed the stepper control module so that every time it sees a 0% request it will carry out a hard reset to re index the stepper, so if it has become " lost " during a low voltage event it will automatically reset to continue correct position control.
To avoid frequent hard resets we suggest your normal operation range would then be 1% to 100% PWM ( at 1% it is effectively shut anyway so you do not loose any useful control range)
If your ECU allows you can also program the PWM range to go to 0% over a certain RPM, such as 3000 RPM.
In this manner the Stepper would re index every time the increases over 3000 RPM so if your stepper became " lost " during a low voltage event then simply blip the throttle to give you over 3000 RPM and the stepper would re index itself to reinstate correct control


 

PWM Signal Type and Frequency

The PWM signal input to this module is the  “ Ground Switching “ type. ( most common ECU output mode ) This means at 0% PWM operation the PWM signal held is High ( 12 volt ) by the ECU and at 100% the PWM signal input is held Low ( 0 volt ) by the ECU
 
The unit is designed to work with an input between 90Hz and 300Hz with the optimum being the commonly used 100Hz output frequency.
Where possible for optimum results set your ECU output to 100 Hz output frequency.

 

Electrical Connections

Connector Pin 1 = Coil 1 Positive
Connector Pin 2 = Coil 1 Negative
Connector Pin 3 = Coil 2 Positive
Connector Pin 4 = Coil 2 Negative
Connector Pin 5 = PWM Input

Connector Pin 7 = 12 volt Power  ( from ignition key or ECU controlled power )
Connector Pin 12 = 0 volt Ground

 

Do I have Stepper Motor Type A or Type B ?

Using a multi meter test for continuity on the two centre stepper motor pins.
= If you results show no continuity then it is probably Type A
= If you show resistance reading of typically 40 to 60 ohms then it is probably Type B
 

Type A motors
Commonly used by GM and after market throttle bodies such as Holley and Edlebrock etc.
Also used in our Webcon Retroject throttle body
 

Type B motors
Commonly used by Magnetti Marelli, Renault and  Citroen
Also used in our combined standalone Idle Stepper motor and housing assembly.