What is causing idling rev & loud screeching sound behind my dash when car warms on 2006 Volkswagen Jetta

My 2006 Jetta revs up, then drops down, and repeats over and over when car idles. Also, after car warms up, or immediately on hot days, there is a loud screeching noise that comes from behind my dash on the passenger side. It has 120,000 miles, and already I have replaced the entire braking system and O2 sensors due to this, but no one seems to be able to guess what the cause is.

Asked by for the 2006 Volkswagen Jetta
I think you got two problems ,the screeching I think is the bearing in the heater motor ,no?.
And they all have that high ,low/ ,problem ,I think throttle body needs cleaning..
Thank you so much! I'm having it looked at next week. I'll let you know how it goes.
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My car was fast revving until the valve gasket cover was replaced. the part cost 172$ from Deutsche Auto part. I noticed on the repair pal the estimated cost including labor could be as low as 150$ not know about the loud screeching noise