When i first start my car, it starts at high RPMs. After about 5 min of high RPMs, It drops to about 1100 RPM. Then nonstop revs from 1100 to 2k. It only happens when I'm in Neutral. As soon as I put the car into first gear it stops. The car only has 145k on engine and body. Ive heard vacuum leak, MAP sensor, Bad Tranny. I don't know where to start.

 

likely a vacuum leak or bad IAC valve. Search on here, there are tons of posts telling you how to diagnose and fix either issue.