I have a '95 miata that I turboed a few years ago. Around last year or so I’ve been having a problem with a hunting idle in warmer weather. Below 50-60F the problem doesn’t occur at all. On days of 90+F it hunts pretty constantly when idling.
I have replaced the IAC, it is unaffected by the AC being on or off. The inch vac looks good (no vac leaks). The TPS checked out fine, the MAF and IAT checked out good and I cleaned the MAF with MAF cleaner, I’ve pulled the whole TB off and cleaned it and made sure the throttle plate was not sticking. I burped the cooling system after the IAC replacement.
I have completely and utterly run out of any ideas of what to look at next. Please help.
Edit: The idle fluctuates between ~1,200 and ~1,800 pretty quickly/violently causing the engine to shake. When it isn’t hunting it sits at a good idle of around ~950rpms.
Edit2: The turbo uses a RRFPR and not a different ECU or piggyback for fuel management.