Frankenstein318

Cooler temps at idle on one cylinder are somewhat meaningless unless one cylinder is consistenly missing; the mixture distribution will tend to change as RPM's go up. You need to run the engine at a constant speed at load to see the variations. And #1 and #2 will tned to be cooler any way, being closeest to the fresh intake air. To make you readings accurate with any infrared temp guage, a spot needs to be smoothed on each exhaust runner and a flat black high temp enamel applied to each spot.

The only thing of significance I would take form the idle exhaust runner temps is if the black soot is out of the side with the cool runner; perhaps that one cyclinder is getting excess gas or has weak spark, and is having the combustion temps significantly lowered.