Idle bounces when it warms up

I live in Oregon and it is cold here.
When I first got my car the temp rarly ever got up off of cold and it idled fast.

I had a new themostate installed and now it warms up , the heater works but after about 1/2 of driveing the idle bounces. 1000-1200, 1000-1200 and just keeps it up.

before it starts bounces it idles around 7-800.

I did bleed the collant and found no bubbles.

Any ideas on how to stop the bounceing idle?

1990

TIA

Bob