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Engine Stalling/Bad Starts/Inconsistent tune


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I am facing a problem with my tune.Have done approx 1700 kms and the car is well tuned.It starts almost fine in the morning,better when is hot,have done the idle procedure and have walked through open loop to closed loop to set the duty cycle of my ISC valve,have engaged Idle Ignition Control,used plennty Autoune and mixture map,pulls hard till 8500 rpm,generaly it rides almost fine.

I have one problem that i can not solve from day one and dont know in which direction should i look...I am circling aroud the things i have done such as adjusting the ISC valve duty cycle.Idle Ignition Control can not solve the issue.Is a mechanical issue, bad idle control valve issue, ECU problem... WTF? 


The problem is that sometimes i have bad engine startups and i should keep the revs with the gas pedal ,tight parking maneuvers are a bitch as the car wants to stall when i let the gas pedal and the most annoying is that when i come to a stop after overrun the idle falls way down low,the AFR's also,to 20's and the car stalls....There is no conflict between overrun,have done the idle procedure correct  many many times and the car other times behaves as it should.So the tune is not consistent.There are days when nothing of this happens.Someone could easilly say to adjust my idle but have done this and my target error is spot on.First open loop and then closed loop.


The car is Alpha N(no map sensor active on the tune) and the IAT reports high but its correct.Have 2 of them,the intake is just above the exhaust header and when i come to a stop heat soaks.What you guys think,before the sledge hammer takes play....


Below are some stalls and my pc link file.These 3 are stallings.




 And these are bad starts






Mazda Miata Current Map with Knock.pclr

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I’m replying from a phone so haven’t looked at the tune or log at all but I will say up front that there is a fundamental flaw in your setup.  If you want to control idle with an air bypass valve then you will need a MAP sensor. Without MAP there is no way for the ecu to know how much extra air is bypassing the throttle to add the correct amount of fuel.  You can still run alpha N, but it will need MAP as the load equation source for idle AFR to be reasonably stable.

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Thanks for the reply. When you have time please OPEN my eyes because I am ready to fill the trunk with TNT... Where or how I can I change this setting Adam? Should I go to Fuel Main->Load=BAP and change that to MAP or somewhere else? I am on Load=BAP right now. The reason for selecting alpha N is that I have vacuum at idle 33~40kpa due to the aggressive camshafts with 106 LSA and 12mmift from 8 mm originally. 


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  • 3 months later...

Happy New Year first of all,to everyone.

@Adamwyou were spot on about the Equation Load Source to use MAP instead of BAP.The car now behaves as it should when i reach to a stop.

I would like to ask the following because i dont get it....On the Link Help file it says to use BAP if the MAP signal is not consistent as mine.I have more or less 30 kpa at idle,unstable due to high lift camshafts.Why BAP couldn't work on my occasion and how could I control my idle if I was using BAP instead of MAP? 

Now that i have selected MAP instead of BAP i can not use the mixture map.It's not showing up?

My PC Link is below.Thanks fellas!

Mazda Miata Final Map 3.pclr

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With load = BAP, you are controlling the amount of fuel to inject based on throttle position alone, so when the idle valve opens and lets extra air in, the ecu doesn’t know so can’t add the correct amount of fuel to compensate.  With load = MAP,  the ecu looks at both TP and MAP, when the idle valve opens, MAP increases so the ecu adds the proportional amount of fuel to keep the mixture close to target.

The mixture map will still work, make sure you are logging MAP.

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