I have one, but it has a low limit. Even with that, 50 degrees difference at cruise won't show much of a difference at idle - if I can catch the damn thing in the act... it's intermittent.

I haven't ruled out a tired IDM either. I'm not saying it's out, I'm saying it might be an idea to try it, then keep the old one as backup if this does nothing. If it works, I can send the old one in for repair. I'm thinking long game here - who knows what price and availability will be, years from now.