Troubleshooting my idle
 

1993 Mazda Miata 1.6L Manual
MS2PNP

Hi everyone,

I installed my Megasquirt over the weekend, and I'm using a GM IAT Sensor with an Innovate MTX-L wideband. Before the install, my timing was at 14*, and started up/idled fine.

Following the install (and loading of the supplied base map), the car started on the first try and idled fairly well, never stumbling while we repeatedly adjusted timing offset and restarted the engine. At the end of the night, timing was 10* and the car idled fine although a little low (500-650RPM). Since I had forgotten to "Calibrate AFR Table", my wideband gauge was reading correct but TunerStudio was stuck at 12.10.

Today I started the car, calibrated the AFR table and took it out for the first drive using Live Analyze; the car ran great and the tune was going well. Only issue was an idle dip when coming to a complete stop. As I pulled into my driveway, the car shuddered and stalled out. It refuses to start again since, unless I give it some throttle. Even then, I have to hold the gas or it'll stall out; it seems to want to idle around 450RPM.

I'm very new to tuning, and I don't really need a "perfect" tune, just something that will get me to work for another week before the car goes into storage for the winter/full turbo install. Can anyone give me some pointers? I'll attach my msq if it helps.

have you tried searching and following the writeups that are out there for it??

lmgtfy Mega Miata: Basic idle settings

To add on, here is what I've tried:

Adjusted Idle RPM target range
Turned Idle screw CCW (this helped the car finally stay idling once I had used the throttle to start and briefly warm the car)
Tried both Open-Loop(warmup) and closed-loop idle settings

Yes, I referred to this but didn't go far; I noticed he was running a 1.8L and his charts had different RPM ranges (his were 620-7XXX, mine are 800-7XXX and couldn't figure out how to change the range)

Mine is an MS1 on a 1.8, but maybe a few of these settings could be helpful to try.



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Check your injector settings if you aren't running stock ones. Make sure the deadtimes are right. Some manufacturers aren't accurate in what they say the deadtimes are.

edit #2...i was looking at the right tune...

-lower your cranking rpm to 300, if your car wants to idle at 450 its staying in cranking fuel. outside of one temp cell its very rich in cranking.
need to work on the cranking pw table

-do you mean to have idle valve set to inverted?

-req_fuel has wrong engine size and no injector settings that i can see

It's getting late here but I just ran outside and tried starting the car with 300RPM cranking speed and it started very nicely, idling around 1,100 gradually dipping as it warmed up. Once it reached about 950RPM, my AFR gauge would spike to about 15.6 and the engine would hesitate (this routine slowly looped).

I'm not sure what an idle valve set to inverted means, but I'll update the req_fuel table tomorrow (iirc, engine size is 1596 and injector settings flow:230cc, not sure about the impedance)

Thank so much for your replies man, you're a huge help!

after setting req_fuel, start the car and use the warmup autotune. it should get you close. once warmed up adjust your idle ve cells to get the AFR you want (13something if batch fuel), then do the warmup autotune the next day.

having your idle valve inverted means 100% = 0 so higher numbers = less open time...normally its the other way around. set this to "normal 0% = off"

Awesome, will do. Thanks (as I eat a bowl of ramen, no joke)