Got a 2002 Honda Civic sedan automatic, the check engine light is on when you start the car then proceeds to blink when going past certain rpms. The main issue is car drives fine when you keep it around 60km/h but when I go on highways reaching only up to 80km/h the car starts to shake like if I were stepping on the brakes every other second. Kinda feels like if someone were to step on and off the clutch in a standard car going 80km/h, it just pushes your body back and forth. I think that it might be a trans problem, I dont have an obd scanner but Im just curious as to what other people might think the problem is. The engine light does blink when the shake happens, aslong as i can remember that car has never had the tranny fluid or auto trans fluid changed no clue if those would help.

 

Most auto parts stores will scan the computer and tell you the codes it's reporting for free (sometimes they will test other parts too - like alternators, starter motors, batteries). I say start there.
I haven't had a problem like this, so it's hard to say without more information.
Usually when a check engine light blinks - it signifies a very serious error. One which is more serious than just having the light on.