Stalling when coming to a stop, only with AC on (REV MS3 Basic) - Miata Turbo Forum - Boost cars, acquire cats.

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Old 05-23-2016, 04:12 PM   #1
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Default Stalling when coming to a stop, only with AC on (REV MS3 Basic)

Odd issue cropped up yesterday. I've made no changes to the tune or car.

When coming to a stop, or coasting with the car in neutral, with the AC on, the RPMs plummet, and the car tries to stall. It can occasionally catch itself, but it usually drops like a rock to zero.


The car runs perfectly otherwise, and recreating the action, with the AC off, causes no issue. So my belief is that the extra load of the AC is the root of the problem? I can post logs of anything you like, it will stall when free reving, the coasting down to idle, with the AC on and the car parked. I have the "AC idle up" stuff enabled, always have.


Current tune should be attached.


Should I be looking for an engine mechanical problem (vacuum leak? although MAP numbers don't look off), since the problem occurred out of no where?


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File Type: msq 2GR VVT Swap Current Tune.msq (243.8 KB, 56 views)
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Old 05-23-2016, 05:29 PM   #2
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Get a log.
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Old 05-23-2016, 05:31 PM   #3
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yup likely the a/c iacv load comps or triggers
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Old 05-23-2016, 09:27 PM   #4
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Log below.

Car started, allowed to settle into idle, 2 revs, the AC engagement. Idle drops (nearly stalls), rev it a couple times, dies coming back down to idle.


I'm re-calibrating the wideband tomorrow, just in case, saw some funky readings today. Had zero issues up to this point, and made no changes.


EDIT: If you want anything else logged, say the word.
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File Type: csv 2016-05-23_20.24.18.csv (137.7 KB, 49 views)
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Old 05-23-2016, 09:32 PM   #5
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Quote:
Originally Posted by 18psi View Post
yup likely the a/c iacv load comps or triggers

NOOB question: Would this change on its own?


I'm basically using a slightly modded base map REV sent me. Worked fine last week. Or am I looking at component failures? 20yo car, totally possible. My experience is with OBDII based diagnostics/testing, so I'm still figuring out MS3.
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Old 05-24-2016, 08:11 PM   #6
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Found my problem.

Minimum RPM for AC idle up setting. My understanding was this was the minimum the ECU would RAISE the idle, to compensate for AC load. It actually is the minimum rpm before AC load is compensated for. At 300rpm, the car would nearly stall before the ECU would attempt to raise the idle to compensate for AC load.
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Old 05-24-2016, 10:15 PM   #7
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Here is screen shot of Manual for v1.4. A/C should not engage below the setting of the "Min RPM for idle up". I think if you got it fixed, it was something else you changed that fixed it. Or it fixed it by disengaging the compressor, not by compensating for the additional load.
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Stalling when coming to a stop, only with AC on (REV MS3 Basic)-80-image_066dc83e4b9478bc350b71bf55b8c5e423f43f70.png  
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