We let the car sit for about 2 months, it had no CEL. We go to drive it one day and we get a ECM code. Car drove perfectly fine, but we didn't want to risk anything so we were going to buy a new one. We still used the car but not very often, one day the CEL was gone. Before we even reset ECM and it still came back, but now its just gone.

What to do?

BTW this is a 1998 sport

 

You should still have stored codes. But after 255 starts the stored codes will clear on its own.