2003 Satarn Vue

I have a 2003 satarn Vue, last year I replaced the timing belt.In the past month the car has been runnig rough at idle on start up and the engine light is on. The code scanner says (misfire on all cylinders).I don't beleave that all of the coil packs can be bad. I have already done a tuneup, checked for vacuum leaks and cleaned the crank sensor.The fuel filter will be my next chioce.Do you have any other suggestions? Pease help