I have a Hyundai Santa fe 2003 2.4L. About a year ago, car check engine light pop up and had a misfire in cylinder 2 and 3. Shop told me they changed the coils. Everything was fine until 3 months ago. Santa Fe shut off while driving a few times. i took it to another shop and they replace timing belt(which was worned ) and crankshaft position sensor was replace too. Everything was fine until 2 weeks ago when check engine light went on again. I have an OBDII reader and its reading PO300 (multiple random misfires, PO302 (misfire on Cylinder 2) and PO303 (misfire on Cylinder 3). I replaced sparkplugs (NGK Iridium IX) and wires were replaced too. Ignition coil replaced (both). About a week from today same codes appear PO300,PO302,PO303. What else could it be??? Also how do I reset the computer???? Any help will be really appreciated. Thanks.