I owned an '01 Civic EX for some time before my dad took it over. He needed the good gas mileage. I had problems similar to that where nothing would be wrong with the car, but the check engine light would come on. I started changing the oil every 3000 miles and checked the plugs on the intake electrical components. If the light was still on after I did both of these things, I would simply disconnect the negative battery terminal and wait a couple minutes before re-connected it to reset the computer. It always worked for me. Hope this can help you.