I'm working on a 3.1v6 and 7730 ecu swapped 86 Camaro. I've been fighting for a while now(before the swaps) a high idle where the car will idle around 1100 at start up then the idle climb to 2000-2500 after you start driving.
The IAC is new and the passages are clean. Tonight I noticed the headers glowing a dull orange after about an hour drive. At idle (170ish coolant temp) cylinder 1 was about 350° while the rest were 450° to 500°.

At 1000rpm idle vacuum is almost exactly 20 in and fuel pressure is 43 psi with key on engine off. All injectors ohm 12.9-13.1

could this be a tuning issue or something mechanical going bad?

 

Yes

 

Ant idea on which, or where to start looking?
My list of possible issues shrinks every time I work on the car.

 

Gm put out a product that works. What's different on your car?
What's been changed recently?
Start answering those questions and that's where you look first.

 

The problem is that the answer to your question is "almost everything" it last ran well before the '302 ecm died( 9mpg no idle no ALDL communication) since then, the ecm, intake, timing, and tune have been changed.