I can't think of another word for it. The RPMs at idle doesn't change much, bounces between maybe 700-800 at the most. This "bounce" happens about twice every second. This is on cold start.
When it warms up, the bounce stops but it develops a mild, intermittent stumble.
Once warmed up, shifting from Park to any gear other than Neutral results in a more pronounced stumble followed by a decrease in idle speed to around 600 rpm. Shifting back into Park results in a brief stumble and then a higher idle (around 900-1000)
Cleaned the throttle body and the IAC valve, not sure where to look next.
Thoughts?

 

could be the nature of the car but if your IAC is clean and functioning properly, next would be to look for cracked vacuum lines/ boot leaks etc and perhaps consider a new ECT sensor + thermostat.