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IDLE CONTROL

An Idle Air Control (IAC) stepper motor valve is used to open or close a passage in small increments (called “Steps”) that adjusts the amount of AIR going through the throttle. The fuel calculation automatically senses the extra air and AFR, so there’s extra torque produced at idle to
increase idle speed or decrease idle speed if the RPM doesn’t match the Target Idle RPM. The amount of steps needed is also learned, in order to improve the idle control.

Warm Idle Speed = This is the Target Idle RPM for when the engine temperature reaches 170 degrees Fahrenheit.

Reset Idle Learn = The Idle Air Learning can be reset to a default value (16 steps) – by setting this control value to 1, and turning the key off and waiting for the system to completely power down. This can be done if the IAC learned incorrect values from an improper throttle adjustment, or other situation that caused the learning to be wrong.

Idle Learn MAX = This is the maximum number of steps that can be learned up. There is a default base table that is used to automatically increase the IAC when cold. There are also 3 learn values for idle air: 20F, 65F, and 170F – this can help the cold engine idle be correct.

Idle Learn MIN = This is the number of steps that can the learning can learn in the closed direction from the base default table.

Loop Rate UP = The IAC uses a PID (actually just PI) closed loop control that adjusts the steps to achieve the desired idle speed. This value controls how quickly it can open the IAC in response to a lower RPM, using the “I” (integrator) of the PID.

Loop Rate Down = The IAC uses a PID (actually just PI) closed loop control that adjusts the steps to achieve the desired idle speed. This value controls how quickly it can close the IAC in response to a higher RPM, using the “I” (integrator) of the PID.

Fan RPM Adder = When the electric fan(s) is(are) turned on, the RPM can be increased by this amount to help both the coolant flow and the alternator speed to generate more voltage for the electrical system.

Fan Idle Steps = When the electric fan(s) is(are) turned on, the RPM can be increased to help both the coolant flow and the alternator speed to generate more voltage for the electrical system. This adjusts how many IAC steps are automatically added when the fan is on so that the loop and learning don’t need to do the work.

Decel Open IAC = When the throttle is opened, the IAC is also opened by several steps in preparation for when the throttle closes. This open IAC helps reduce engine braking during deceleration which can give a smoother drive feeling. However, too much can cause the RPM to jump a bit too much when the throttle is cracked open, or cause the engine to have positive torque for a moment after the throttle is closed.

Decel RPM Decay = When the throttle is closed, and the engine is returning to idle speeds, the Idle Closed loop will use Target RPM to control the speed during that period. The Target RPM will decay to the normal idle speed in a controlled manner. A smaller “Decel RPM Decay” value will be SLOWER.

Decel IAC Decay = When the throttle is closed, and the engine is returning to idle speeds, the “Decel Open IAC” steps will need to be removed in a manner that nearly matches the “Decel RPM Decay” of the Target RPM. This value is the fraction of a step that is decayed per 100 milliseconds (10 times per second).

CRANK IAC = Cranking needs extra air to help the engine spin to a higher RPM and to generate very full cylinders for maximum power to fire up the engine against the cold oil. However, at warm engines, the thin oil and easy combustion doesn’t need as much air to achieve a successful start, and too much will cause a very large flare of the RPMs just after starting.

45 comments on “IDLE CONTROL

  1. MeanStreet system, I have idle set to 900RPM but its controlling it to 1400rpm.

    1. It sounds like the TPS may be reading high causing the system to not recognize your idle. Please follow the instructions below.

      Turn the driver’s side throttle adjustment screw IN (clockwise) half a turn to start with, with that done turn the key on and go to dashboard and find TPS and make sure it reads zero. If not, then shut the key off and wait for the numbers to go black then turn the key on again. Once that reads zero start the vehicle and find IAC Steps on dashboard. This number needs to be within 3-10 at warm idle. If the number reads zero then slowly turn the screw OUT (counter clockwise) until the IAC steps reads between 3-10. If the number is above 10 then shut the vehicle off and turn the screw IN as stated above and repeat the process until the IAC steps are between 3-10.

  2. I have an IAC question. I recently had changed my IAC steps to read between 3-10 its usually around 5-6, I started it up a couple days later and now it reads 45-55 on the IAC steps and it wont come back down. My RPM is around 850-900 right now. Its not increasing the RPMs that much even though its really high on the IAC steps.

    Thanks
    Nathan

    1. IAC steps being between 3-10 only matters when the engine is at operating temperature in park or neutral. Depending on engine temp and load on the engine your IAC steps will be different. All we are after is that your IAC steps are not excessively high and unable to control your idle. From what you are describing the system is doing a great job of maintaining your idle rpm.

  3. Hi, with the 30002, Is the system will adjust the idle to the minimum when the AC is turned on?

    1. Whatever you set the warm idle speed at in the engine setup of the handheld your engine will run. The idle control maintains the idle speed regardless of the load on the engine. This applies to when the AC is on vs off, electric fans on vs off, and transmissions in park vs neutral.

  4. Just installed the go EFI 400 with the command center. It runs great except when I jap the gas it kind of falls on its face I have tried different settings on the accelerator pump but not successful

    1. Refer to the Basic Setup page of the website. In there you will see how to adjust the accel pump.

  5. I am having a hard time with idle . The engine seems to be loading up and cuts off . The iac at warm idle is 175 pluses or minus . How do I get this fixed

    1. Follow the IAC adjustments in the link below.

      https://fitechefi.com/tech-posts/fitech-efi-basic-setup-instructions/

  6. I am having a issue with the car still kinda running after I shut her down. I have read everything I think but may have over thought and over looked my answer. A little help? Thanks

    1. Be sure your cutting power to the white wire at key off. Also see what your idle AFR is. If you enriched it up too much you can cause the engine to diesel.

  7. the car starts and acts just like it did with the carb at cold start, super rich, dose not even come close idling, dies, have to restart time and time again, after it’s warmed up I had the iac steps down around 7 to 10 as it should,so?????? at a bit of a loss, the motor is a sbc 350 with a pretty big cam aluminum heads air gap intake, headers exhaust, so any help would be great!!!! thanks rich.I do need to tell you that I have not put any miles on the car, can this be part of the problem?

    1. Leaning out your target idle AFR would be a good start. When you say you have a big cam what are the specs? lift, duration @ 50, and LSA.

      1. sorry I took so lone to get back to you Bryce, the cam spec’s are comp cams dur @ .050 250/256 110.0 lobe lift – 519/523 I hope this helps. each time I start the car it dose seem to get I bit better. my car is in primer so I cant drive the dam thing in the rain and I live in Washington state, this time of the year that could be a long wait. ha. thanks for any info man, I really want this thing to work as it should!!

        1. Adjusting the cranking fuel should resolve your issue. Also try leaning out your target AFR at idle to around ~14.5 to lean our your engine. You have a decent size cam so removing fuel at a low RPM will help.

  8. I HAVE JUST INSTALL FITECH EFI8 SYSTEM ON A 572 BIG BLOCK & HAVE BEEN ADJUSTING IDLE/IAC & CAR IS OVER FUELING BAD?

    1. Is there a full length exhaust on your vehicle? Also how much vacuum does your engine produce?

  9. Hi Fitech Support.

    I have installed the 600 Kit and Command Center a few weekends ago. I got the IAC set to 3-10 after normal warm up and the car runs fine now after getting warm. My question is on cold start. I have played with he settings, currently crank 20f= -10.9, 65F= -16.4 and after start 20F=8.6 and 65f=9.4 but still having a few issues. The car will fire on first try but then die. I have adjust these settings up and down but have had no luck. If i give it some throttle durring cranking then it will start and after about 30 sec start to idle fine and go into normal warmup mode. This makes me think I need more fuel during the cold start phase but when i go up buy 10 on each of the settings the car seems to have a harder time even. I have a CompCam 270H in it currently and I am on Cam selection 2. Any help would be greatly appreciated.

    1. You clearly have added more fuel but have you lowered the amount of fuel you give the engine? Also what is your base timing set at?

  10. Can system #30002 be used for an Air Conditioned car application? (Double checking because I saw it mentioned on forums that only #30004 can be used for AC). Thank you!

    1. Yes you can. You only downside is the 30002 EFI will not turn on an electric fan when the a/c turns on.

  11. I have a new fitech 30002 the iac steps are at 200 any ideas its flooding like crazy

    1. It sounds like you need to open the throttle more to get your IAC steps down. Also check for fault codes as well as check for vacuum leaks and AFR readings being close to the target.

  12. I’m having trouble maintaining a steady idle. Running a GM502 idle set at 900 rpm. The idle stutters every 5-10 seconds dropping by 200-300 rpm. It always catches itself and overcompensates bumping up to 1000+ for a second or so and then settling back down at 900. This cycle repeats over and over again indefinitely as long as the you are in idle. IAC steps are between 5-10 at idle. idle AFR is set to 14.0. When the drop in rpm takes place, AFR leans out to 15/16. Any advice would be great.

    1. This sounds like a vacuum leak. Also check your base timing.

  13. I have the Go-Street system on 195HP Chevy SB from GM Goodwrench. With ambient air temperatures anywhere below about 40 degrees, upon cold start the engine fires immediately then dies immediately. From there it’s a dance of opening the throttle and closing it while cranking it to get it to start. Upon it starting, it runs very rough before I kick it up to a higher RPM (about 2500) then let it come down to find it’s programmed idle. At this point, it’s very finicky to start. Suggestions?


    1. PLease follow the instructions in this link for adjusting your crank and warm up fuel, it seems you need less fuel on start up when the car is cold.

  14. Hi, I am having trouble finding information on resetting the passenger side throttle body adjustment screw for the secondaries (I do see the process for setting the driver’s side). I will be resetting my tune from scratch and have adjusted the secondaries screw in the process, and would like to set it back properly. I have the Go EFI 4 600 hp unit. Thanks

    1. Turn the secondary screw counter clockwise until it no longer touches the throttle stop, then turn the primary counter clockwise until it no longer touches, then turn the primary screw in one and a half turns after it touches. Then turn the secondary screw in to where it just touches the throttle stop. that should reset you to factory. PLease make all your future idle adjustments using only the primary screw.

  15. I Have Go Efi 4 system, I have idle set to 800RPM but its controlling it to around 1400rpm sometimes jump to around 2000rpm, IAC reads 0 jumps to 1 and 2. ( between zero and 1 and 2-3) mostly at zero
    I have tried to follow the instruction in the first post
    TPS is zero and try to turn the screw out but nothing happens ? IAC doesn’t change .

    1. If your idle stays high and you backed the throttle adjustment screw out all the way you definitely have a vacuum leak. Check all of the vacuum ports on the throttle body as well as any vacuum consuming component.

    2. mine car is doing the same thing, Ive checked every where for a leak but I cant find one, Did you resole your issue?

  16. I have the Go Street 30003 and the Fuel Command Center on my Chevy 350 Van. It works great except it is way too slow returning to idle. Hardly any engine braking. In “Go EFI Tuning,” Idle control does not show “Decel open IAC” on my handheld controller. Is there another way of adjusting idle return? My idle control window shows only three items, 01 Warm Idle Speed, 02 Reset IAC Learn, and 03 Reset TPS Learn.

    1. The EFI is designed to catch the idle 300 RPM above the target warm idle speed and then bring it down slowly itself.

  17. I just installed a Go Street EFI on a Toyota 22r 4cyl motor. Is there a way to change the number of cylinders to 4 on initial setup so the tac reads correctly. I was able to get the idle down to 1000 rpm by cutting idle parameters down to 500 on the programmer. Also the idle screw is backed all the way out and still have a reading of 0 on the idle air control.

    1. Follow these steps to load a 4 cylinder calibration.

      1. find “Write Cal To ECU” on Main Menu
      2. Select “Default L4 T195O” file
      3. hit enter on joystick to load file.
      4. When loading finished key off for 30 seconds.
      5. Go through Engine setup to finish your setup.

  18. I have a 454 chevy engine in a 1962 c 30 truck .put the600 horse unit on it not to hard except it want start unless you prime from a gas can the electric fuel pump is producing 55lbs 0f preasure as a closed loop .After its running and warm .it still doesn’t strart What do I do?

    1. Have you adjusted the throttle? If not this would explain your hard start issues. Here is how you adjust the idle in regards to IAC Steps.

      IAC Steps:

      Turn the driver’s side throttle adjustment screw IN (clockwise) half a turn to start with, with that done turn the key on and go to dashboard and find TPS and make sure it reads zero. If not, then shut the key off and wait for the numbers to go black then turn the key on again. Once that reads zero start the vehicle and find IAC Steps on dashboard. This number needs to be within 3-10 at warm idle. If the number reads zero then slowly turn the screw OUT (counter clockwise) until the IAC steps reads between 3-10. If the number is above 10 then shut the vehicle off and turn the screw IN as stated above and repeat the process until the IAC steps are between 3-10.

  19. I have a dual 4 650 units every thing is great except start up . It won’t fast idle up on cold or warm start.

    1. You will need to adjust the throttle using these steps.

      IAC Steps:

      Turn the driver’s side throttle adjustment screw IN (clockwise) half a turn to start with, with that done turn the key on and go to dashboard and find TPS and make sure it reads zero. If not, then shut the key off and wait for the numbers to go black then turn the key on again. Once that reads zero start the vehicle and find IAC Steps on dashboard. This number needs to be within 3-10 at warm idle. If the number reads zero then slowly turn the screw OUT (counter clockwise) until the IAC steps reads between 3-10. If the number is above 10 then shut the vehicle off and turn the screw IN as stated above and repeat the process until the IAC steps are between 3-10.

  20. Installed the 400 hp model on a 351 ci ford. I can get it to start and after 30 sec or so it shuts off. Even with the throttle open some it still shuts off.

    1. Check fault codes which is option 7 or 8 on the main menu. Also check for loose wiring connections.

  21. if I am having cold start problems should I lean out idle afr

    1. You need to check and adjust your IAC steps. If they are between 3-10 at operating temp in park or neutral you will need to adjust your cranking fuel in the section Crank And Warm-up.