5.4 Idle valves 5 SETTING UP A BASIC CONFIGURATION
• Closed loop - The ECU moves the valve as needed to target a specified idle speed.
We recommend only selecting a closed loop idle mode after getting the engine running well in an open loop mode.
Open loop commands how to open the valve as a function of temperature, while closed loop targets a specific idle
speed.
Once you have selected a mode, you will need to set up the individual IAC modes. Settings not used are grayed
out.
5.4.1 On / Off settings
• Fast Idle Temperature - the solenoid opens below this temperature and closes above it.
• Hysteresis - If the temperature drops below the opening temperature, it needs to drop by this additional
amount before re-opening the valve to prevent the MS3Pro from pulsing the valve rapidly at the opening
temperature.
• Output port - Select which output you wish to use to control the solenoid.
5.4.2 Stepper valve settings
• Time Step Size - This is the number of milliseconds the firmware will wait between each step. If a valve does
not move reliably, this setting should be increased.
– If the valve is perfectly dialed in, this will match the time it takes the coil move the motor through a single
step. If this value is too low, the step is not completed, and the valve does not move. If the step is too
high, the valve will move more slowly than it can - but it will still work, so it is better to set this too high
than too low. Your best bet is to set this for 10 ms, then decrease until the valve no longer moves. Then
add 0.5 to 1.0 ms.
• Initial Time Step Size - When moving more than one step, using a larger time for the first step can help
overcome stiction in the valve. Setting this larger than the Time Step Size can improve reliability.
• Minimum # of steps to move - This is the minimum number of steps the controlling piece of code has to
command before the code that moves the valve will actually try to move the valve. We’ve found some stepper
valves, particularly used ones on older cars, may stick if commanded to move fewer than 5 to 8 steps.
• Homing Steps - This is the number of steps the valve will move (in the closing direction) on power on so that
the rest of the code can rely on the start position being accurate. After retracting to the Start Value, the IAC
valve will then move to the number specified in the Cranking Steps.
• Homing Direction - Specifies if the valve opens or closes during the homing time.
• Wide Open Steps - If the valve is set to home in the opening direction, this sets the number of steps between
closed and wide open. The number of homing steps should be larger than this to ensure reliable operation.
Not used if the homing direction is set to closed.
• Crank-to-Run Taper Time - This is the amount of time the IAC valve uses to transition after starting from its
crank position to its running position. Not used in closed loop control.
AMP EFI MS3Pro manual version 1.202, firmware 1.5.0, 4/21/2017 Page 98
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