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Old 10-04-2014, 10:43 PM   #1
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Default MS1 Extra idle oscillation


I've been having trouble with idle oscillation. Its mostly stable, but sometimes after the car has been running for a while the idle rapidly bounces from 1000-1500 RPM. The setup is a braineak built MS1 Extra on a 1995 1.8 with A/C.

I read many helpful threads on idle here, but honestly don't know what to start adjusting. I had it professionally tuned a while back but they didn't get this quite right, so I wanted to reach out here for help!

Can anyone point me in the right direction? My best guess is that idle control settings are incorrect.

A side question I had is about the algorithms for idle, do these vary across releases of Megasquirt?

Any suggestions/comments welcome, thanks
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MS1 Extra idle oscillation-untitled-28.png  
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File Type: msq UMS Power tuning 1.msq (35.9 KB, 39 views)

Last edited by hellothere; 10-04-2014 at 11:03 PM. Reason: Say thanks
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Old 10-05-2014, 12:42 PM   #2
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I occasionally had issues with this too. I ended up going with warmup PWM so that the valve only moves when the car is cold, and raising the idle RPM in the summer months. Try to get it stable with warmup PWM first before you play with closed loop, that way you'll find the idle advance, AFR, and RPM that will keep it stable.
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Old 10-05-2014, 08:58 PM   #3
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Ah ok great thanks for the tip! I'll start with the warmup PWM and see what I can get. Did you have base settings to start with? Would you kindly share the idle settings you're running?

I added a screenshot of this happening. The throttle is at 0 but RPMs are hopping all over.

I was under the impression that closed loop is required to offset the A/C compressor drag. This might not be needed though? It seems correct closed loop settings with this software hack is a good MS1 setup MS1 AC Idle-Up Code Hack
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Old 10-06-2014, 08:21 AM   #4
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read hornetball's idle tuning for ms1 thread.

edit: looks like you already have.
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Old 10-06-2014, 10:26 PM   #5
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I did read his epic hack of adding idle A/C support to MS1.

I understand idle settings are tuned to engine specific configuration, but
shouldn't there be a baseline for a Miata 1.8l?

People seem to have luck with the settings Joe Perez posted Megasquirt idle issue - MX-5 Miata Forum

I'll try the warmup and known good closed loop settings. If all is well I'll
also try the code hack so I too can have OEM idle with MS1.

PS there are many posts about idle issues. It might be helpful to have a sticky
on somewhere here.
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