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Old 11-06-2010, 12:54 PM   #1
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Default Lowering idle speed

Hey everyone, Now that I won't be needing the AC for winter I've decided to drop my idle back to the <1K range but something is off. Basically I have to lower my Minimum(dc) to 9 just to get the car under 1K RPM at idle. I thought it could be a vacuum leak but I've checked with smoke and starter fluid and havent been able to locate anything. Unfortunately when I set Closed(dc) and Minimum(dc) to 9 to lower the idle the car stalls whenever I come to a stop. My idle adjustment screw is closed all the way because if I open it any I have to lower the Minimum and Closed to maintain a decent idle speed which seems to exacerbate the stalling issue.

My car is a 1997 Mazda Miata with a JRSC kit (TB before the blower)

My settings are

Minimum(dc) - 9
Closed(dc) - 9
Slow Idle Speed - 850
TPS Threshold - 25
Idle Activation - 700
Dashpot Settle - 75
Dashpot Adder - 1

Upper Limit - 200
Lower Limit - 50
Fast Recovery - 3
Slow Recovery - 39
Closure Speed - 2

Any advice would be appriciated. I've just noticed that most people have Minimum(dc) around 20-25. Would the low Minimum(dc) have anything to do with the stalling issues?
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Old 11-06-2010, 03:40 PM   #2
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Hail Mary Bump
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Old 11-08-2010, 12:24 PM   #3
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Have you tried increasing the Dashpot Adder value? This briefly adds more duty cycle when the throttle is snapped closed.
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Old 11-08-2010, 12:37 PM   #4
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I raised it to 4 with no effect.

Yesterday I disconnected the IAC and manually set idle at 800. Then I plugged it back in and adjusted the values enough to keep it from stalling (or oscillating wildly) and I've managed to get a fairly stable idle at ~1050. If I lower anything by even a point it droops to ~300 and then sways like crazy. I changed my fast idle RPM settings but that either led to a stall or more sway.
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Old 11-08-2010, 03:59 PM   #5
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What is your voltage at idle? What are your AFRs? Have you considered a dual TB setup? Try forcing it rich at idle.
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Old 11-08-2010, 04:08 PM   #6
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Voltage is around 13. I did run it rich which didn't seem to help but when I pulled spark it calmed it down a bit. My spark advance is 9 in the box where it usually idles and 10 surrounding it.

I havent considered dual TB but I am thinking about moving the TB back to stock position and putting a blow off valve on the blower. I think part of my problem is that when the TB closes there's still a ton of air in the intercooler piping that it can't quite compensate for.
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