7.4 Startup / Idle 7 ADDITIONAL ITEMS: BEYOND BASIC FUEL AND IGNITION CONTROL
• Idle Valve Minimum Duty or Minimum Steps - This specifies the lowest duty or number of steps, below
which changes in the opening position no longer affect RPM. The closed loop control will not set the IAC
valve to a lower number.
• Idle Valve Maximum Duty or Maximum Steps - This specifies the highest IAC position beyond which further
changes do not affect RPM. Note that intentionally setting this low can make the closed loop idle a bit less
sensitive and more stable.
• Dashpot Adder - The MS3Pro will disengage the closed loop idle based on TPS or other criteria. Once the
TPS reading falls below the value set by “throttle closed TPS threshold” in Engine State Settings, the MS3Pro
will add this amount to the current IAC valve opening to prevent the RPM from falling too quickly and making
the engine stall.
• Use last value or table - If “Use last value” is selected, the MS3Pro will start with the value it last used
to obtain the target RPM when closed loop idle re-engages. If set to “use table,” when the closed loop idle
engages, it will select the initial idle opening from the Closed Loop Idle Initial Value table.
• Use CLT or MAT in table lookup - This specifies if the initial value table uses coolant or manifold air
temperature to determine the initial value.
• Close delay - This setting controls how long in seconds the valve takes to go to the closed position after the
throttle is pressed. A setting of 0 seconds means do not close the valve.
• Open valve on WOT - This setting causes the idle valve to open if the TPS value goes above the wide
open throttle threshold value specified in engine states. We’ve seen this produce measurable power gains
on engines where the throttle body is slightly undersized and the motor needs all the air it can get.
• Leave Valve Closed Above (rpm) - On throttle lift, leave the idle valve closed above this RPM. Note: This
setting is only necessary if a close delay is set since otherwise, the valve does not close when the throttle is
pressed.
• For this number of seconds - This setting re-opens the idle valve after the number of seconds set on throttle
lift/shift. After this timer runs out, the valve will open to the previous learned value plus the dashpot adder.
This is used to allow the valve to closed while shifting gears, but to open the valve in cases where this may
be necessary to prevent stalling.
Closed loop idle PID gains are used to tune the response of the valve. We’ll go over the tuning process after
covering the remaining settings.
• Tuning Mode - In Basic, the P and I terms are set to 100, the D term is set to 0, and the slider is the only
adjustment. In Advanced, you can adjust the gains separately, and then they can all be scaled with the slider.
• Proportional Gain This setting controls the Proportional Gain of the PID algorithm. Setting this higher
will result in a larger immediate response to changes in RPM. Setting this too high can result in unwanted
oscillation of RPM.
• Integral Gain This setting controls the Integral Gain of the PID algorithm. This is the PID setting used to
actually make the RPM meet the target RPM. Setting it too low will cause the RPM to never reach the target.
Setting this value too high will result in unwanted oscillation of RPM.
• Derivative Gain This setting controls the Derivative Gain of the PID algorithm. It can be used to help dampen
the effects of the Proportional and Integral settings. It is usually not necessary for good control of idle speed.
It is recommended that this is left at 0%.
Closed Loop Idle PID Delays and Behavior - These settings cover more about how the engine reacts to a given
amount of valve opening. The code has two adjustments, a sensitivity slider that affects response with a single
adjustment, and individual PID gain adjustments for engines that need more detailed changes.
• PID delay - This is how long in seconds all other conditions for entering PID control must be met for before
the MS3Pro will engage PID control. Set this as low as possible without being below what is normal RPMdot
jitter with the engine RPM not changing. Typical values will be between 50 and 75 RPM/sec.
• Crank to run taper - How long after starting the MS3Pro will wait to engage PID control.
AMP EFI MS3Pro manual version 1.202, firmware 1.5.0, 4/21/2017 Page 185
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