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Discussion Starter · #1 ·
I'm evaluating some different ways to change my idle RPM. Has anyone tried to use a donationware software like TunerPro with a SkyActiv? Other than some older Miata's, I couldn't find any definition files online. I've also thrown around the idea of dumping the file and trying to find the variable manually with a hex editor. It tends to be hard to guarantee you've got the right encoding, variable, updated CRCs, etc, so I'm not holding my breath on that, although I'd love to hear if anyone has had luck with that on any modern ECU. I would consider mazdaedit if I wanted to change maps, but I can't justify the cost to be tied to one vehicle I just want to change the idle speed on. If anyone has came up with any clever solutions, I'd love to hear them. I realize its a longshot. Taking it to the dealer may end up my best option.

For the curious, I just want to raise idle speed slightly to lower vibration with an aftermarket mount.
 

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Theoretically if there is an RPM signal the engine uses, piggybacking with uC at idle, reducing the frequency slightly, may result in increased idle speed. ;) ... and other issues may happen too.

Better mount with damped design? Years ago I made a cradle mount for vw transaxle on my kitcar, using two part high durometer urethane. It worked excellent.

https://sites.google.com/site/kitcarlsonems/
 

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Discussion Starter · #3 ·
Thanks! The Aztec kit car is pretty impressive. It looks like you've done a lot of tuning on it.

Using a microcontroller to spoof RPM is a good thought. Another hardware solution also occurred to me. Since this is a fly by wire vehicle and the throttle is really just a potentiometer, I could make a simple opamp circuit with a trimpot to always keep the throttle on just a bit. I'm sortoff doing this already as I'll tweak the throttle after I get to a stoplight to avoid idle. Changing the variable in ecu memory would be a little more eloquent though. It might be wise for me to go ahead and eat the $80 cost of an openport, dump the rom, see if I can find my way around it. If not (likely) I could always have the dealer make the change, dump rom again, then diff the files and see what changed. At least I could change it simply in the future if I wanted.

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TPS systems typically have redundant pots and reverse slope channel too. Throttle closed is also derived from min value,and compensates. Fooling idle speed would not happen as you think, Idle speed is controlled via air bypass valve, and ignition timing, both via ECU closed loop systems.
 

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Discussion Starter · #5 ·
TPS systems typically have redundant pots and reverse slope channel too. Throttle closed is also derived from min value,and compensates. Fooling idle speed would not happen as you think, Idle speed is controlled via air bypass valve, and ignition timing, both via ECU closed loop systems.
Interesting. I had expected dual channels, that would be easy enough to address. From what you're saying though, it sounds like the throttle self calibrates, and any change I might make to the min value will be calibrated out? I could believe that though. I might be able to get around that with something as simple as a fast idle switch, click it on whenever I use the A.C.. Not truly raising the idle speed as you've pointed out, but I believe the effect is the same? Regardless, that solution is getting more convoluted even compared to your rpm spoofing suggestion.

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I am not sure that what I sugested will work. The system likely derives RPM, from raw crank position data,change may throw codes, if redundant checks are in place for OBD. Cam sensor data could also be used. RPM change would also change economy, emmisions.... auto trans.

The A/C is also under ECU control.
 

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Discussion Starter · #7 ·
All good to note, thanks. Changing in ECU would be the most eloquent method. Will be weighing my options.
 
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