My Corolla 2014 has this issue where revs fluctuate quite a bit at idle, sometimes dropping to 4-500 revolutions and going back up. I changed the MAF sensor, cleaned the throttle body, replaced the air filter, replaced spark plugs, and it still does it. Also, there’s no CEL or codes. I took it to my mechanic and they couldn’t find anything wrong with it.
What could it be?