Idle Control

The MS3 firmware has several methods for controlling idle speed:

• On/Off Valve - This Is for controlling a simple on/off valve.
• Warmup-only modes

  These modes are open-loop and only control valve position based on coolant temperature.

  • IAC Stepper Always On - Leave IAC stepper power on even when not moving.
  • IAC Stepper Moving Only - Power up IAC stepper motor only when necessary for moving.
  • PWM Warmup - PWM valve in warmup only mode.
  • 15-minute IAC - Power up the IAC for 15 minutes for warmup, then power it down.
• Closed-loop modes

  These modes are closed-loop. The user must set a target RPM curve, and several other settings to determine when the code goes into closed loop mode.

  • PWM Closed Loop - PWM idle valve in closed loop mode.
  • IAC Closed Loop Moving Only - Closed loop IAC mode where the IAC motor is only turned on when the valve needs to move.
  • IAC Closed Loop Always On - Closed loop IAC mode where the IAC motor is on whether the valve needs to move or not.

Each mode is described in detail below.

On/Off Valve

The On/Off Valve idle speed control option is the most simple control option included in the MS3 Firmware. It includes the following settings:

• Fast Idle Temperature - This is the temperature below which the idle valve is turned on.
• Port - This is the output port to which the idle valve is connected.

Общие настройки прогревочного и постоянно-повторяющегося режимов работы РХХ

The only common settings between Warmup-only and Closed-loop control methods are the cranking position curves. That curve sets the position of the PWM controlled idle valve during cranking, depending on the coolant temperature (PWM idle has nothing to do with cranking fuel pulsewidth):

Common Settings for all PWM-based valves

All PWM-based modes have certain settings which are shared:

• Valve mode - Possible Settings:
  • Normal, 0%=off - This means that 0% duty turns off the idle valve.
  • Inverted, 100%=off - This means that 100% duty turns off the idle valve.
• Output Port - Possible Settings:
  • FIDLE - Use the standard fast idle pin on the main MS v3 board.
  • Idle - Use the fast idle pin on the MS3X board.
• 3 wire mode - This mode is used for three-wire idle valves, such as those offered by Denso and Bosch.

  Possible Settings:

  • Off - Do not use 3 wire mode.
  • FIDLE - Use the FIDLE port as the second control pin.
  • Boost - Use the Boost control pin as the second control pin.
  • VVT - Use the VVT pin as the second control pin.
• Valve Frequency Selection - This setting is used to select between 1.5KHz mode and reduced frequency mode. Some valves will not work at the high 1.5KHz frequency, and for those it is necessary to use the reduced frequency mode.

  Possible Settings:

  • 1.5KHz - Set the valve frequency to 1.5KHz
  • Use reduced - Use a reduced frequency. Possible Frequencies are listed in the reduced frequency item.
• Reduced Frequency - This setting should be used for those valves that do not work at the higher 1.5KHz frequency setting.

  The following frequencies can be selected:

  • 780Hz
  • 390Hz
  • 260Hz
  • 195Hz
  • 156Hz
  • 130Hz
  • 111Hz
  • 95Hz
  • 85Hz
  • 76Hz
  • 69Hz
  • 63Hz
  • 59Hz
  • 54Hz
  • 50Hz

Warmup Only Modes

The Warmup Only options are open-loop modes that set the IAC/PWM valve to a specific position based on the Coolant temperature. The user must set each temperature and a corresponding valve position in a curve:

All warmup-only modes also have the following common setting:

• Crank-to-Run Taper Time - Time in seconds to go from the crank position to the run position.

The four warmup-only output options are detailed below.

IAC Motor Common Settings

The IAC Stepper modes all have several common settings. Those settings are detailed here.

• 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.
• 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.
• Start Value - This is the number of steps the valve will move (in the closing direction) on boot so that the rest of the code can rely on the start position being accurate.

IAC Warmup Moving Only

IAC Warmup Moving Only is an open-loop algorithm which sets the valve position based directly on coolant temperature. Keep in mind that this mode turns off the valve between each set of steps. If the valve does not work reliably in this setting, it may be necessary to use the Always On setting. In addition to the common IAC motor settings, this mode also has the following setting:

• Initial Time Step Size - This is the number of milliseconds the firmware will wait after turning on the idle valve before trying to move the pintle.

IAC Warmup Always On

This mode is exactly the same as IAC Warmup Moving only, but does not have the Initial Time Step Size setting since it leaves the valve turned on all the time.

15-minute IAC

This mode is exactly the same as the other IAC Warmup modes, but leaves the valve on for 15 minutes after start, then turns it off.

PWM Warmup

This mode works functionally the same as the IAC Warmup options, but for a PWM valve instead.

Closed-loop Modes

The MS3 firmware employs a PID (Proportional Integral Derivative) method of control for controlling idle speed to meet the user-specified target RPM. Target RPM is specified in a Coolant-temperature-based curve. Common settings for all closed-loop modes as well as options specific to each type of valve are listed below.

Closed Loop Common Settings

A curve for setting the target RPMs based on coolant temperature is used by all closed loop idle-speed control modes. All other idle-speed control settings are listed as well:

Settings common between all modes are listed here:

• Closed Loop Idle Valve Settings -
  • Idle Open Duty or Open Steps - Idle Open Duty and Idle Open Steps perform the same function for PWM closed loop and IAC closed loop respectively. They specify the duty or number of steps at which the idle valve is fully open. This can be set lower than the fully open position in order to limit the maximum value to which a valve will open.
  • Idle Valve Closed Duty or Closed Steps - Idle Valve Closed Duty/Steps specify the duty or number of steps at which the idle valve is fully closed. This can also be set to the minimum valve position that the user wants to use for a particular setup.
  • Dashpot Adder (percent or steps) - This setting sets the amount that the valve is opened above the previous known-good valve position calculated by the PID algorithm when PID control was last engaged. The dashpot adder is added to the last known-good position each time throttle is lifted.
  • 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.
  • 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. For example, if the throttle is lifted, and RPM is above the Leave Valve Closed Above setting, the valve will stay closed until the value set for this setting expires, then the valve will open to the previous learned value plus the dashpot adder. The purpose of this setting in combination of with the Leave Valve Closed Above setting is to keep the valve closed when shifting gears, but open it on longer overrun events.
• Closed Loop Idle PID Delays and Behavior -
  • Min duty/steps for PID - This is the minimum duty that the PID code will use while engaged.
  • RPM with valve closed - This should be set to the engine's RPM with the idle valve closed.
  • RPM with valve open - This should ideally be set to the RPM with the valve fully open. It can however be set lower than this value to increase the sensitivity of the PID algorithm.
  • PID delay - This is how long in seconds all other conditions for entering PID control must be met for before the code will engage PID control.
  • Crank to run taper - How long after starting the code will wait to engage PID control.
  • PID ramp to target time - This setting controls how long after the PID control algorithm engages the code will take to reach the target. The code starts with an RPM target of whatever the current RPM may be, and then slowly over the ramp to target seconds reduces the target to the value set using the target RPM curve. This can be used to help larger P-values be used, making it easier to tune PID to catch sudden drops in idle speed.
  • PID Control Interval - This controls how often the PID control code runs. Values of 100ms or less will normally give the best control. Values that are too long will make the code respond too slowly to sudden changes in load, possibly allowing the engine to stall.
  • PID disable RPMdot - This setting was added specifically for those who sometimes engage the clutch while rolling to a stop after letting the PID code engage. Set this setting as low as possible so that when RPM suddenly jumps when the clutch is engaged, PID is disabled and does not try to close the valve due to the RPM suddenly going up.
• Closed Loop Idle PID Gains -
  • 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 Activation Settings -
  • Use VSS to activate PID - This setting controls whether the PID lockout settings (detailed later) are used to activate idle speed control, or if VSS going to 0 MPH/KPH is used.

    Possible Settings:

    • Standard
    • Use VSS
  • Idle Activation RPM adder - This setting controls the RPM below which the PID algorithm is engaged, and the RPM above which PID is disengaged, and the close taper (if a Close delay setting is used, detailed later) is started. This setting should be set in the 200-300 rpm range for best performance.
  • Idle Activation TPS threshold - This setting is the throttle position below which the PID algorithm is engaged. It is used in conjunction with the RPM adder to determine whether or not to engage PID control of the idle valve. This should be set as low as possible to avoid the idle valve closing when the throttle is pressed.
• Closed Loop Idle PID Lockout Detection - These settings are used in a situation where due to uncontrollable factors (IAT changing, load at idle changing while not in PID control, etc.), the RPM gets "stuck" above the target RPM + adder setting, causing PID not to engage. These settings will allow this condition to be detected causing the code to enter PID control anyway.

  The following settings control the behavior of PID lockout detection:

  • PID Lockout rpmDOT threshold - This setting controls the rate of change of RPM above which the code will assume that RPM is actually really changing (as opposed to RPM changes just being normal slight jitter in the engine RPM). Set this just above the maximum rpmDOT seen when the idle gets stuck above the target + adder threshold. Values of 50-80 are typical.
  • PID Lockout max decel load - This setting controls the kPa below which the PID lockout detection code is disabled. This should be set to a kPa just under the lowest kPa that is seen during a fast idle.

PWM Closed Loop

This setting applies the above settings to a PWM Idle valve.

IAC Closed Loop Moving only

This setting applies the above settings to an IAC motor. In this mode the motor will only be turned on when it is commanded to move. The IAC motor common settings from the warmup-only section apply here as well.

IAC Closed Loop Always on

This setting applies the above settings to an IAC motor. In this mode the motor will be on as long as the MS3 has power. Use this setting if Moving Only gives unreliable results. The IAC motor common settings from the warmup-only section apply here as well.

Tuning Recommendations

Before trying to tune closed loop idle speed control, be sure to try tuning warmup only idle speed control. With warmup only control, a higher step-count or duty should yield higher RPM. Make sure that this is the case, and that smooth idle speed can be attained with warmup only before moving on to closed loop control.

There are two main things to tune when tuning closed-loop idle speed control:

• PID gains
• Conditions for entering PID control

It is recommended that tuning is done in stages. For example, PID cannot be tuned if the code is never entering the PID loop. Because of this it is a good idea to start by tuning the conditions for entering PID control.

These settings include:

• Use VSS to activate PID - This takes the place of the PID lockout settings. Turning this on will make it so that the PID loop activates after the vehicle speed comes to zero MPH/KPH.
• Idle activation RPM adder - Set to 200-300 RPM for best algorithm performance.
• Idle Activation TPS threshold - Set as low as possible. If the TPS has a bit of noise, set it to around 1%, otherwise set it to 0.3%-0.5%.
• PID delay - This should be set so that the RPM dropping on throttle lift can come to a rest slightly higher than the target RPM, and become stable there. Between three and five seconds normally works the best.
• Crank to Run Taper - This setting controls how long after starting the code will delay before entering PID. Between three and five seconds works well for this setting.
• PID lockout rpmDOT threshold - This is the first of the PID lockout detection settings. Use this setting so that the code can tell the difference between decelerating with closed throttle (engine braking) and sitting at one RPM. 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.
• PID lockout max decel load - This is the second PID lockout detection setting. The code assumes that if MAP is lower than this setting, the driver must be decelerating, and not "locked out" of the PID loop. Set this to a value just under the load seen with an idle slightly higher than the current target RPM + the Idle Activation RPM Adder. This can be done by temporarily switching to warmup-only mode or idle test mode, and setting the valve position manually.
• PID disable RPMdot - A good value for this setting will typically be in the 200-400 RPM/sec range. If the engine speed suddenly accelerates with no throttle input (like if the clutch is engaged while the car is rolling and in gear), it must accelerate at a rate greater than this setting before the PID code will be disengaged. Setting this value too high can lead to stalls after engaging the clutch in this manner.

To tell whether the code is entering PID idle control, the "CL Idle" indicator in TunerStudio must be used. If the current gauge cluster in TunerStudio does not include this indicator, temporarily switch to a cluster that does.

Most modern OEM cars enter idle speed regulation in a very similar manner. The MS3 idle speed control algorithm was designed to emulate this behavior. The sequence of events that the code was designed to follow are listed below:

1. Throttle Lift - On throttle lift, the code opens the valve to the value learned in the last iteration of the PID loop + the dashpot adder. The logic here is that the last learned value should result in an RPM close to the target RPM. The dashpot adder is added so that when RPM settles, it settles to an RPM slightly higher than the target. This is in case the air conditioning was turned on or IAT increased or anything else that might make RPM lower than the last time the PID code ran.
2. RPM settles - After throttle lift, eventually the clutch is pushed in and RPM drops to wherever it will settle given the learned value + the dashpot adder. Hopefully the idle has settled to an RPM that is less than the commanded target + the Idle Activation RPM adder. IF so, then the code will wait for the amount of time specified by the PID delay, and then enter PID control. If RPM settles above the commanded target + Idle Activation RPM adder, the code then starts checking the PID lockout detection conditions. Assuming those condtions are met, the code will still enter the PID loop after the amount of time specified by the PID delay.
3. PID control activates, RPM starts dropping to target - After the PID delay expires, the PID code will be activated. RPM will slowly drop to the target over the number of seconds specified by the PID ramp to target time.
4. Normal idle speed reached - RPM reaches the commanded target. PID continues regulating RPM until the throttle is pressed.

Once the code is reliably entering PID on every throttle lift, it is time to actually tune the PID code to reach and hold the RPM target.

The settings that are associated with or affect the operation of the PID algorithm are listed below:

• Idle Open Duty/steps and Idle Valve closed duty/steps - These should be set to the minimum and maximum values that should be used during PID loop and driving operation. In addition, having these set further apart results in the PID loop being more sensitive (making changes to the output given much smaller changes in input).
• Min duty/steps for PID - This is the lowest duty/number of steps that the PID loop is allowed to command. Set this low enough to result in an RPM slightly lower than the lowest target RPM.
• RPM with valve open/closed - These should be set to the RPM with the valve closed and the RPM with the valve opened respectively. If using these settings makes the code unresponsive to changes in idle speed, the upper RPM value can be set lower.
• PID Control Interval - This controls how often the PID code runs. Setting this too high can result in sluggish response to sudden changes in load, such as the Air Conditioning being turned on. Setting it too low can result in the loop being overly sensitive to RPM changes. Typically 100ms works well.
• PID controller gains - These control the actual response of the code to changes in RPM, as well as how well the code will reach the target. Tips for tuning these are listed below.

The following basic steps should be used for tuning the PID controller gains:

1. Zero all the gains - Set all the gains to 0%. This is so that the effects of tuning the I-term in the next step are not confused with the effects of any other setting.
2. Tune the Integral (I) gain - The Integral gain is the only term that controls whether the code actually reaches its target. Higher values for Integral gain will result in the code being able to get closer to the commanded target; however, a value that is too high will result in oscillation. The easiest way to determine a good value for the I term is to keep increasing it until oscillation occurs, then slightly lower it. If this value is increased to 200% without reaching a point where oscillation occurs, then the RPM with valve opened setting can be decreased as far as necessary, and the open duty/steps setting and closed duty/steps setting can be made further apart to make the PID loop more sensitive.
3. Tune the Proportional (P) gain - After tuning the I gain so that the RPM reaches the commanded target without oscillation, the P gain can be tuned. The best way to tune this is to set it as high as possible without getting any oscillation. After setting this, try turning on the air conditioning or other accessories that normally lower RPM or increase load. When these accessories are turned on, the RPM should dip a bit then recover (the valve position should increase significantly). Using longer PID ramp to target times can also make it so that when the PID algorithm engages, a higher P gain can be set without causing oscillation.
4. Tune the Derivative (D) gain - For most users, use of the D gain should not be necessary. It substantially dampens the response of the loop.

Some final tips:

• Idle Fuel Tuning - Before even attempting to tune Closed-loop Idle speed control, tune the area around idle so that if RPM goes up or down or load goes up or down, the AFR stays close to the same value. Changing AFR can affect idle speed, which can then cause the PID code to try to correct, getting into an unrecoverable oscillation.
• Idle Advance - The idle advance feature can be used to help "catch" the idle in situations where heavy load is suddenly added while the engine is idling. It is recommended that the advance is increased with increasing load, and decreased with decreasing load. This way when the air conditioning or electric fan are turned on, the sudden increase in load causes a corresponding increase in timing which generates more power. Also, this feature can be used so that on idle without load, slightly less than what would normally be considered "optimal" timing can be used. This causes the idle valve to need to open further to keep a particular idle speed. Then when sudden load is added, the timing increases and the valve position does not have to change as much to cope with the sudden load increase.