I've got a 2003 Mazda 6. 2.3L. Car was running fine. Next day it was idling rough. Acting like it was going to die. So I replaced the o2 sensors, spark plugs, spark plug wires & coil pack. It started fine. Sat there for 20 minutes and no problems. Put it in gear and now it's back to the same idling issue. I did all the things the mechanic told me to. What am I not doing?