ECT code popped up. Began with high idle in hot weather and stalled at stops...

What is your question?

1999 honda crv 2.0L auto with 284k miles. Problem began with high idle all of a sudden while driving and stalling at stops. Thought it was idle air control valve but only code to show was etc...turned idle down...made no difference. Returned idle to previous position. Code for etc came up and after consult with mechanic...told to change electronic temperature control sensor. When etc removed...car quit stalling at stops and runs great except rough starts with car stalling only at initial start of day or if sits for long period of time. When etc replaced with new etc sensor....car goes right back to wavering idle and stalling at stops. Is it the idle air control valve...or is there a cheaper resolution prior to spending so much money on parts I don't need? I saw on a few prior posts that it could be a vacuum leak, coolant probs...etc. Please help. Have had 3 mechanics tackle this issue and its still unresolved. Daughter really needs her car back. Thank you.