My Miata has recently been going into a weird idle cycle where it will idle up to 2000rpm and then sit there and bounce from 2000-2100 over and over. It does it randomly and isn't consistent with it being cold/hot. Some days it won't even do it and idle right at 900rmp and others it won't idle correctly at all. Wondering if you guys have any ideas about what would be causing this and what I could check? Searched but couldn't find any threads that addressed an issue like this. Thanks in advance.

 

IAC valve sticking? Or one of the little vacuum switches has a line leaking when it is switched open. Or maybe the temp switch is starting to fail and telling the engine to go into warmup enrichment.