6.1 Getting started 6 TUNING THE MS3PRO
• Idle Valve Homing Steps - This only applies to stepper idle valves. This setting determines how many steps
the motor should move during homing to ensure it has reached the home position. The number needs to be
large enough to close the valve from any unknown starting position. (This is because there is no position
feedback on most automotive stepper IAC valves.)
• Idle Valve Step - the desired valve position if using a stepper IAC valve. Larger numbers should give a more
open valve and higher rpm.
• PWM idle duty% - the desired valve position if using a PWM IAC valve. Larger numbers should give a more
open valve and higher rpm.
(Note that some Bosch rotary PWM valves valves feature a failsafe mode so that zero flow is at a midpoint, such
as 20% duty,; above that the valve operates as expected where more duty gives more airflow. Below this specific
point is a failsafe mode that allows airflow even if there is no control signal. This is readily observed during test
mode.)
There are three control buttons:
• Enable Test - Home Position - for stepper idle valves, this moves the valve through the number of homing
steps back to the home position. (If it doesn’t get all the way back to the stop, increase the number of homing
steps.) The valve will move to the run position shortly afterward.
• Enable Test - Run Position - enable test mode where the steps or duty setting controls the valve position
• Enable Test - In/Out Cycle - Cycles the valve continuously between the homing and run positions.
• Stop Testing - disable test mode and allow normal idle control to operate.
Testing a stepper IAC valve First, click the Enable Test - Home Position button, and verify that the valve
closes completely. The valve will move back to the run position on its own; if you are doing this test yourself and
want to make sure the valve is closed, set the run position to zero. Stepper valves can be a bit more complicated
to troubleshoot than PWM valves. Here are some common problems and what to do if you encounter them.
• Problem: Valve vibrates when commanded to move, but does not actually turn.
– One coil is wired backwards; swap wire 1A for 1B, or 2A for 2B.
• Problem: Valve moves, but in opposite direction of intended.
AMP EFI MS3Pro manual version 1.202, firmware 1.5.0, 4/21/2017 Page 103
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