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High Idle with odd "bounce"

Old 05-14-2019, 03:55 PM
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Default High Idle with odd "bounce"

The "Bounce"
While idling at ~1800rpm the engine will die for an incredibly short time, AFRs will drop (from 14.7 to 22.4), RPM will drop (from ~1800rpm to ~1600rpm) and then everything returns to the where it was.

Drive the car around (nothing strenuous) to warm her up. She is warm by my standards and the MS. So there is no enrichment as far as I can see.
However I do see the "No fuel cut" indicator flash red each time it "bounces".
So something is causing this but I cannot see what.
The aggravating part is this happens for seemingly no reason. I can reproduce it (most of the time) by driving around until warm or longer, turning off then back on however that is not how i logged.
I was happening when i pulled up to the garage so I recorded it then, no stop start affair just plain happened.

I am running TunerStudio Ultimate 3.0.28 and am on firmware 1.4.1 using a Reverant MS3 Basic.
I have only fiddled with:
  1. the rev limit (7300 instead of 7000)
  2. the VE table (bit of VEAL and a bit of MLVHD)
  3. setup the IACV properly (or at least according to the guides on here).
My little Phoebe is a 1992 1.6 long nose Eunos imported into UK.
Stock engine aside from 4-2-1 header that was cheaper than OEM.

Its not a vacuum leak.
I've always had it since install I just assume it was something to turn like the IACV but i've done that.

Additional Information
I've attached my tune as basic as it is and a log.
I took the log on my drive while doing literally nothing.
Feels like a fuel cut but for what i have no idea.

Any ideas would be greatly received?
Attached Files
File Type: msq
CurrentTune.msq (274.9 KB, 8 views)
File Type: msl
2019-05-14_16.50.43.msl (359.2 KB, 7 views)

Last edited by rrjwilson; 05-15-2019 at 04:55 AM. Reason: Trying to clarify things
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Old 05-20-2019, 04:30 AM
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This is still occuring and I do not know why. Anyone?
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Old 05-20-2019, 08:40 AM
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You are activating the overrun fuel cut. Reduce your idle valve cranking PWM duty by 6% to begin with. Then fine tune the closed loop idle parameters so that closed loop idle doesn't activate while you are actually driving - if CL idle activates while you are coasting down in gear, it will increase the idle valve duty and you will activate the overrun fuel cut while it idle because the revs are so high.
Originally Posted by ninerwfo View Post
The “into to megasquirt thread” mentions that the MS3 basic has 5 inputs with built in pull up resistors - and I was just wondering why it would have so many, while the MS3Pro PnP has just 2 (with no pull ups?)
MS Labs: Plug and Play Megasquirt ECUs for ANY 90-05 Miata (NA, NB1, NB2 w/VVT, MSM), including basemaps to get you started ASAP. PM me or email or details.
For support on MS Labs ECUs: Please email, be sure to include the unit's serial number and include a datalog and your current map.
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Old 05-21-2019, 05:18 AM
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Cheers Rev I'll have a look.
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Old 05-22-2019, 09:54 PM
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Also: Your overun fuel cut "Map Lower Than" is much too high.

It's set to 28KPA with a .7 second delay - this matches exactly with when overrun activates in your log.
Set your "Map Lower Than" setting to 23 or 24 and it'll settle down.

Note: to see overrun activate in your log use a custom field named "Fuelcut On" (or something like that) with a calculation of "([Status3] & 1)"
Note: depending on your firmware, that might be "Status3" or "status3".

Last edited by VcrMiata; 05-22-2019 at 09:59 PM. Reason: Rev's comments still apply, this is in addition
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