Very good, detailed information, Bob. Thanks.

I'm on the CLEAN side. Field testing? Sheesh---difference was night & day when we cleaned mine.

And the reasons for replacing rather than cleaning boil down to the almighty dollar. There's more profit in selling a $500 part than the $20 you'll make cleaning it... I hate the "dixie cup" answer to everything these days: don't fix it, just replace it. Like cell phones, nobody has them fixed. If they **** up, just get another one...

What about IAC valves. Clean or replace?

PCV's?

IAC valves can be cleaned, and they're not cheap to replace.

PCV valves are easy enough to clean, but they're cheap enough to change once a year or two.