my issue was fixed after the temp sensor was replaced

 

I had the same problem for a long time, so i finally looked into it more and more and found that it was my IAC valve, and when i replaced it i realized why, because it was a metal gear on the inside and a plastic one in the IAC so it basically stripped it out. Good luck

 

Sounds like your mechanic isnt very intelligent! He should be able to rule out most of those sensors you have listed by reading a computer. With an aftermarket tune, you would want to start there, but probably not the issue. Most temp sensors wouldnt be the issue if it happens on cold and hot starts. IAC could cause it, EGR stuck open could cause it... Have someone who knows how to read a scanner and see if anything doesnt look normal.