Idle issues when engine is warm
 

Hello, so I put my Miata away for winter, and recently got it out. On the way home, when the engine was warm, I noticed that the idle dipped below 500 and up to 1100 rpm. When it was put away for winter there were no issues. I have read about possible issues, but the more I read the more possible issues come up. When first starting the engine, no idle issues exist, it only starts fluctuating once it has warmed up for about 5 minutes.

So far I found:
IVAC, vacuum leak, idle control valve, o2 sensors, coils, spark plugs, gasket leaks, idle drop problems, various other sensors, etc.

If anyone has had similar issues and could point me in the correct direction it would be greatly appreciated.

Edit: No check engine light is on. I have not scanned it for codes yet, but that will be one of my first steps I do.

what ECU?

Stock and has never been touched to my knowledge.

do the gnd and ten idle adjustment procedure.