I put a new timing belt and water pump on my car a week ago, and a few days later my cel came on. The car runs fine, but has a slight vibration at idle, which it didnt do before. Ive replaced the plugs, cap,rotor, fuel filter and have reset the computer numerous times and it still pops up after an hr of driving. Ive also checked my timing and its bang on. It seems like a missfire

What could it be?