02 5.3L rough idle when cold; occasional, but steady check engine light

[KBM123]

Hello all,
I have an 02 K1500 Suburban with the 5.3L that starts fine, then begins a rough idle once the engine settles down to about 600 rpms after 10 seconds. The problem goes away after it reaches normal operating temperature. A steady check engine light comes on once in a while. (I don't have a code reader) No problems with starting, re-starting, stalling or acceleration, either cold or warm. Gas mileage might be down slightly, by 1 - 1.5 mpg.

I ran a bottle of Chevron with Techron but that has not helped.

Any ideas?

Thanks,
Kenwood