Hi, thanks in advance for any help you can give. My father just bought a 07 Envoy, runs good except once in a while upon start up, it will not come off of the high cold idle. Will not drop down to 6-700 until you shut it off. Doesn't always do this, sometimes upon cold start up, once engine warms up, runs fine and idle drops. These darn "sometimes" issues always drive me nuts. No pattern with temp outside. Can be 10 or 60 degrees, same thing. Any ideas on where to start?