Car idles at about 1500 rpms for about 5-10 minutes when first started. It eventually drops to about 700 rpms after it warms up. Seems like that is too high in both instances. I have removed IAC and cleaned and also replaced t-stat. What would cause this?

What is your question?

Car runs fine otherwise. I can’t find any vacuum leaks either.

What makes this problem better or worse?

Definitely worse when cold

How long has your 1998 Lexus ES300 had this problem?

Since I bought it a year ago. Other than that, it runs great