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There are several systems working together to stabalize the idle. They all have there own set of performance ranges to control. If any get out of the controllable range, then problems like this occur.
O2 sensor, air pump, ACV, cold start fuel map, fuel correction map, and base fuel map all work together to control idle AFRs. The O2 FB switch turns the O2 control it off or on. Running a RECALC also ruins this O2 system.
ISC, Throttle Adjusting Screw, Air Adjusting Screw, and Idle RPM settings control ilde rpms.
Idle IG Control switch controls idle timing which tries to fine tune the idle timing.
"YOU" have to learn what does what and how to adjust them to improve your idle.
But if you mod you engine to some undetermine point, no matter what you do, they will not work as Mazda desgined them to do. Then you have to turn them off and go to a manually controlled fixed idle. Most single turbo guys have had to do it.
With O2 FB and Idle IG control turned off, the ISC will work better. But then you will have to tune your idle and cruise AFR for best smoothness.
When I went single turbo, I did this and ran 550/1300 injectors with the ACV still working as a source of air to the MP/cat which is after the O2 sensor. My ISC worked fine at all three settings.
Then I went 550/1600 injectors, removed the ACV, plumbed the air pump output directly to the MP/cat, and removed the purge valve for the gas tank. After that, my ISC would only work on electric load. I checked eveything including cleaning the ISC solenoid.
I could not get it to work. I went full manual idle control.
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