What could be the reason why my check engine light is on?

Hi, in my car(1999 chevy malibu,4 cylinder) check engine light is on, and it is shaking when car is started & drive with lower than 20Mph. when i shown to some of known mechanics they said problem in coil set & i must reply the hole set because in my car the total 4 coil in one set. Can you please help to solve the problem it's great help to me. Thanks in advance regards Vijay 5103632852

If you have a spark tester or insulated pliers you could verify spark at each tower. The wires could also be tested. The easiest thing would to take it to a parts store and see if it is a misfire code. Don't change any parts until it has been verified as to what the cause of the fault.