Hi,

To make sure all 4 cylinders are running, I unplugged the high voltage
wire from each spark plug (one a a time, not all at once). Each time
the idle RPM dropped a little bit, so I said "OK, each cylinder must be
firing properly".

However, I drove later to AutoZone and asked them to check the error
codes, and there were NONE! not a single error code. So why there were
no error codes? Also, with one wire unplugged, the Check Engine light
did not come on (the lamp is OK, it comes on at start-up).

All this is for a 97 Civic LX by the way.

Thanks