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MS3X NA M20B25 Base Tune that idles well?

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    MS3X NA M20B25 Base Tune that idles well?

    I tried the base MS2 tune from DIYAutoTune and it won't idle above 500rpm. Anyone have another one I can try? Not sure if this is an issue related to MS2 vs. MS3 settings & tables.

    If anyone has an MS3 base tune of any kind I'd be very appreciative if I can take a look.

    I"m trying to tune it correctly, but it would be helpful to have a reference when doing it.

    (Timing was confirmed with light, car has E36 TPS, running on distributor w/ coil triggered by MS3X SPK-A, wideband)
    Last edited by citizen_insane; 05-10-2018, 06:52 AM.

    send me your msq, ill take a look at it, what do you have for injectors?


      Originally posted by 2002tiiguy View Post
      send me your msq, ill take a look at it, what do you have for injectors?
      I will, thank you much, I really appreciate it.

      I'm running the stock injectors. From what I can find online they appear to be 14.2 lb/hr (150cc/min)


        After talking with 2002tiiguy and reading some more forum posts online, it appeared the issue could be related to VR signal dropout. After inspecting my logs, I do see that RPM drops to 0 and then fuel spikes every time I get a hiccup in the idle. Still not 100% sure which one is the chicken and which one is the egg though...

        I took a high speed log using the Tooth Logger and not exactly sure how to interpret it. During the idle portion the pulse frequency aligns with the indicated RPM (100 ms / 600 rpm), but there are some areas where there is a delay between the signals. Now if this were actual signal dropout, I would expect the distance between pulses to be >2X the standard pulse freq, but this is not what's happening. To me this looks like the engine actually slowed down during the 180ms pulse.

        I also checked to see if "rising edge" or "falling edge" made any difference in the idle. It did not. Data logs for both conditions are here:


          As suggested on the MSExtra forums, I opened the ECU back up and turned the VR amplifier trim pots all the way CCW (there's not detent, so I just turned them like 40 turns) and now the system is working. Now i get no tach sync with rising edge and full tach sync with falling edge. After making these changes, the car idles smoothly and recovers fine during rundown. However, the idle is still low ~650rpm.

          Correct settings:
          - VR Trim Pots turned all the way CCW
          - Set trigger on "falling edge"

          I suspect an issue with the IAC, does anyone know how high you can rev the engine with the IAC alone? One guy on the MSExtra forums said his M20 would rev to 3500 with the valve fully open. In my case the valve is set to full open all the time (90% PWM) and I get max 650rpm. Possible issue?

          I finally drove the car around the block, so if anyone wants to see the datalog & MSQ:


            Car runs fine now. If anyone is curious, the reason for my problems was stupidity. I installed the intake tube too far up the elbow and was blocking the IAC intake. Turns out, when you don't do that, the IAC does in fact have the ability to rev the engine to ~3500 rpm. Good to know.


              Sorry i didnt get back to yiu sooner, glad you figured it out