Can u check the code on a 93 with the car running? My check engine light is only coming on after u drive it for a half mile. When u stop and turn car off and check it there is no codes. U can rev the engine but still no code.
You can't check the codes with the engine on but a code should be stored in the memory until the memory is cleared. When the condition exists, the computer stores a code like its taking a note and then illuminates the CEL. When the condition no longer exists, the CEL goes out but the code remains in memory so that it can be extracted.
The only time I have seen your issue happen is when I forgot to remove the paperclip I was using to short the clip and pin on the diagnostic connector. The CEL would blink on or off intermittently while driving.