Hey i got the same issue.
1996 Sierra 1500, 5.7L v8.

I get a blinking engine light at first start up when trucks cold. Code reads Random misfire, Heated oxygen sensors, Idle air control system fault. Truck idles high (1000 rpm) as soon as i put it in drive and start going light go's away. once she cools off it comes back. truck runs great, has no misfire (even tho it throws the code) Ive checked for intake leaks and vacuum leaks, replaced plugs, cap and rotor, then distributor all together. wires are in good conditions.

Any help???

 

96 gm used what most refer to as spider injection system most likely cause is number 4 injector is acting up runs about 70 dollars for new one at parts store or cheaper of order online maybe it's located in the upper intake will need replacement gaskets for lower and upper intake possible o ring and a new injector and should fix issue of course thats my best educated guess going off what you said hope this helps