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Old 12-14-2009, 11:26 PM   #1
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Default Idle setup q...

Ok, I'm going through the idle setup manual and everything goes great until the car warms up so much that the fan kicks on. Then the idle starts to surge and I can't correct it with the idle closed loop settings (proportional, intergal and differential gain)... Up until then, I have a nice stable idle at around 950 rpm and AFR's around 15.

What do I do when the damn fan kicks on and I can't catch the surging?

Thanks,
-Todd
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Old 12-15-2009, 12:02 AM   #2
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beats me, i just idle it rich since i can't figure it out
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Old 12-15-2009, 02:54 PM   #3
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post your map.
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Old 12-15-2009, 04:12 PM   #4
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Quote:
Originally Posted by swimming108 View Post
beats me, i just idle it rich since i can't figure it out
Its probably a lean spot just above your idle cell. Pay careful attention to how the fuel cells are spaced and what MAP you are at. Because the computer interpolates between every cell you can run into issues with raising one cell to much without raising others. With your car maybe the extra load of the fans causes the engine to go into a much leaner condition because the next cell up is actually too lean, and your idle cell is too rich. This causes the motor to loose power and then loose RPM's dropping into the rich area again which makes it gain power. The oscillations start from there and just grow.

Most idle problems like that are fuel MAP related, but the PID settings can also play a role.

Best,
Travis
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Old 12-15-2009, 11:10 PM   #5
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Tweaking the fuel cells around idle helped a lot with some wandering that was occurring when I had my headlights on... But, no matter what I do, it goes nuts when the fans kick in.

As a last ditch effort, I raised my target RPM to 1100 at 90c, no difference. It goes nuts, then dies if I don't jump on it.

I've attached my map...

Thanks!
-t
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Old 12-16-2009, 12:33 AM   #6
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sound just like my problem
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Old 12-16-2009, 01:06 AM   #7
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I don't have mine sorted yet, but this gave me a good understanding behind the theory of how PID controllers work:

PID controller - Wikipedia, the free encyclopedia

In particular this section:

PID controller - Wikipedia, the free encyclopedia

Keep us updated with how you go! I'll do the same when my engine is back together and I get to fiddle with this stuff again.
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Old 12-16-2009, 04:40 PM   #8
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Did you set up your open loop idle values correctly? They are a little way off .

You must read this thread https://www.miataturbo.net/forum/t40771/
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Old 12-16-2009, 09:09 PM   #9
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Obviously my comments only apply to the closed loop stuff, you need to get open loop sorted first...
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Old 12-16-2009, 09:33 PM   #10
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Quote:
Originally Posted by ismael_pt View Post
Did you set up your open loop idle values correctly? They are a little way off .

You must read this thread https://www.miataturbo.net/forum/t40771/
I think you hit the nail on the head... I wasn't sure about my open loop idle settings. I'll work on it this weekend when I have some good time to set up my open loop idle, then redo the closed loop.

It's actually not bad right now... As long as the fans stay off, it idles happily along at around 1000 rpm and is quite driveable (no stalling, surging, etc...)

Thanks!
-t

Last edited by micagreenmachine; 12-16-2009 at 09:51 PM.
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Old 12-19-2009, 07:29 PM   #11
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Wow... Much better... Once I got open loop set well, closed loop was much easier. It isn't even too bad when I turn on the A/C. Tweaking the fuel so it doesn't go lean with an increase in MAP was a big help too.

A little more tweaking is needed, but I can live with it the way it is for a while.
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Old 12-19-2009, 10:46 PM   #12
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Glad to hear things are better now. Can you tell us what you changed in the open loop setting to improve your idle issues?
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Old 12-20-2009, 12:20 PM   #13
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Adjusted my base idle value
Leaned out the idle area (0-60kPa/1-1500rpm), but made adjustments in the tuning table to smooth out the idle area a bit and get rid of any really lean or rich spots right around idle speed/map
Re-adjusted the idle screw, it was too far out (too far counter-clockwise)

I just had them way out of whack, especially the idle screw... Serves me right for trying to rush through it the first time. It's idling around 900rpm (warm) at 14.5ish AFR now and the fan coming on doesn't freak it out any more. I'll tackle the cold idle this afternoon.
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