My 96 Z28 has a missfire I can not locate. The miss is apparent while driving fifteen or twenty minutes. After I shut the engine off for thirty minutes or so the misfire will be pretty much gone, just returning sporaticly. Thinking it was a plug, I installed new plugs. They all looked good although they had about 50,000 miles on them. The plug wires are MSD and new about 40,000 miles ago. Other than a "Service Engine Soon" warning when it is missing, I get no codes.

 

The flashing SES light (if that's what it is doing) indicates a misfire that could damage the cat. That alone should at least set the random misfire code, and possibly a misfire code for a specific cylinder. Further, a scanner with "GM enhanced parameters" capability can pull up the misfire count by individual cylinder. The would at least tell you where to look.

If you don't want to use that approach, have the ICM checked at an auto parts store. Make sure they get it hot while testing, because it sounds like it may be breaking down due to heat soak.

 

Injuneer, thanks for the quick reply. I'll call around and see if I can locate a GM specific scanner.