1990 pontiac subird 2.0 error code12

Code 12, isn't actually a trouble code, its a starting point, and ending point for the diagnosis system. when it flashes its telling you ok we're starting the diagnosis and when it flashes again its saying ok its completed. its the codes after the 12 you are looking for.

As for the hard starting when cold, could just need a tune up. The fuel pressure may be low. Compression could be low. I would do a compression test to make sure.

I hope this helped give you some ideas on things to check.