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Old 10-25-2015, 10:08 PM   #1
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Default Tuning a DIYPNP in a 90's 1.6L

Hi Everyone

Just like to say its the first time i have posted to any forum so please go easy.

I am helping a friend with his 1990 Miata. I got dragged in as i am an electrical engineer so i built it and help to install it and he is a second year mechanic.

So we changed ECU, installed turbo with inter cooler, removed MAF sensor and replaced with IAT and hooked up the baro sensor, changed to innovative 2 wide band.
Haven't yet sourced a VTPS. still trying to talk him into that.

So the issue is we have tried and tried but we still cannot get it to idle correctly. When it does it is running over 22/1 AFR as well as it does bounce, have tried locking timing to 10 btdc and using table, tried leaning fuel mixture, it will always bounce and eventually stall.

Basically can someone who has a similar setup have a look at the msq file and suggest something we can try.

Thanks in advance.

Semi Working.msq
2015-10-25_15.50.28.msl
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Old 10-25-2015, 10:17 PM   #2
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If I had to guess I would say your idle valve is way out of range and causing problems with predictable idle control.

My car seems to like 28-38% for Idle valve duty, but that can change with the throttle body bleed screw. If you go way too far above that range, I believe the PWM driven solenoid maxes out and actually chokes airflow. You're trying something like 70%, I think the most I've ever used was 50-52%...

Try getting the idle up around 1000-1200rpm while it's cold, then see if your adjustments in the VE table make a difference.
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Old 10-25-2015, 11:18 PM   #3
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Thanks, ill try today or tomorrow and let you know how i go.
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Old 11-01-2015, 05:47 PM   #4
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Sorry i took so long to reply.
We tried your idea and it did make a positive impact on the idle...
But.
As i worked out the car would start, rev up to about 1500 Rpm and the slowly drop off until in fell back into the cranking range and then would kick back up to 1500 Rpm again.
Solution: set fuel pressure reg at 3 Bar instead of 1 as recommended by the spec sheet.
i feel like such a D**k.

Anyway we finally got it idling and your suggestion of changing the idle valve duty got us there so much quicker.

Another question. If closed loop idle is set for 1100 at 80dC why once it warms up to 80 does it idle at 600 Rpm? Slightly short of cranking.

Also would you know why when to tap the throttle the car just about stalls and then revs real high even after you release the throttle? but if you hold it it can maintain a higher rpm?

Any help would be greatly appreciated.
Thanks Again.
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