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Idle up on start up?!?!

 
Old 01-18-2017, 09:16 PM
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Unhappy Idle up on start up?!?!

I've searched the forums with no luck. I am relatively new to tuning I have a '94 Miata running a megasquirtPNP. Ever since i put in the megasquirt I have had this strange idle up when starting the car. Its happens almost every time. The car will immediately rev up anywhere from 1900 to 2500 rpms and hold that for a few seconds (from 3 to 8, this changes too), then drop down to ~900. Sometimes it does not do it at all but 95% of the time it does. I am in open loop idle and have messed with all the idle settings to try and get this to drop but found myself frustrated and just dealt with it. The part that i just cannot understand is how inconsistent it is. The only pattern I have figured out is that it will generally hold the idle up longest when it is cold out. I have searched for vacuum leaks and found none. My idle valve PW stay constant throughout the idle up. Any ideas? Much appreciation to any replies, thank you!!
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Old 01-18-2017, 09:22 PM
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Check CLT idle curve

also - miata IAC has an inversion on the low end, calibrate IAC open and closed positions

test cold start valve
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Old 01-18-2017, 09:32 PM
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Would the CLT idle curve be the same as the WUE curve? Also what do you mean by "inversion on the low end", just for education's sake? I will calibrate the sensor though and see if that helps.
Thanks
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Old 01-18-2017, 09:37 PM
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No, not the same

there is a point with the IAC where a reduction in the dutycycle results in a higher rpm. The control system expects lower duty cycles to result in lower rpms, so it responds by decreasing the duty cycle, which results in a higher rpm. It will decrease the DC until it hits the programmed closed position.
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