I think he has had lean codes. And misfire codes. I think someday soon I will have to go over there and we will have to find the bolts and see if we can tighten them.
Weird thing about he ABS and Traction Control lights is that they don't produce codes. He has a (fairly basic) code scanner and nothing comes up related to those two lights.
a bit of advice to anybody looking to trouble shoot there car
get down to a autozone or advanced or napa or what have you
and pickup a OBD code reader
that will make your and our lives much easier
as for the idle problems on that envoy
first thing I would check is the IAC valve and TPS sensor
as well as check the coolant sensors
If you have a basic scanner it is very likely that it won't read ABS or airbag/body codes. If it is an intake gasket leak you can get a can of carb cleaner and spray it around the intake gasket sealing area with the engine running, it will either rev up or misfire a bit when it's sucking the carb spray into the engine. Don't forget to check pcv lines/vacuum lines too. There's one big one on the left front corner of the air intake tube on top of the valve cover. If that has returnless fuel delivery it probably doesnt really have any more than that. Any unmetered air intake to the engine will set that code.
That envoy is new enough to be drive by wire. No more IAC. coolant sensors don't really do anything anymore either. Intake air temp sensor and ambient air temp sensor handle that stuff now iirc.