My daughter's '02 Zetec engine is doing the same thing, but her car has been doing it when it's over 90F.
The plastic thermostat housing just blew out on her last week & she had to have it towed to a garage near her house (as opposed to back to Dad's Garage). That was $90 for towing & $350 for the thermostat & housing replacement. :'(
WNTWN, are you describing the location of the IAC valve or of the PCV & its vacuum line?
"Help, Mr. Wiza-a-ard!!"