LAKEGUY72

I have a 1993 Corvette with 27000 miles on it. After sitting a few days it starts normal, runs like a bear for 10 minutes(idle or on road) then starts popping out of the leftside exhaust. At idle you can hear the pop/pop/pop and when you give it gas it bangs loudly. After about 60 minutes of sitting or 10 minutes of driving it runs fine all day long. During the pop/pop phase if you do a restart it sounds like the spark is over advanced and you hear a click and then it starts. This all seems to start at 195-205 degrees. It's like clockwork-exactly 10 minutes from cold startup after 3 or more days.
No SEL, No codes, no sparks in the dark, no sign of leakage from water pump,no bubbling in radiator.no steaming. Idle RPM is steady. OBD1 scan shows nothing is wrong(O2 sensors,CTS,etc). All grounds checkout, tried packing ice around ICM/coil. vacuum lines not cracked or leaking. Injector balance test ok. If I drive it everyday--no problem!! I'd hate to change the opti without being convinced that's the problem. It still gets 26+ MPG.
Anybody seen this before?
Tomorrow I will run until it starts popping and pull a few plugs to see if any are wet(water/fuel?)
Thanks