I have currently ran into a problem with the engine skipping when it gets warm. I originally did a heater core flush and it drove for a while before it started skipping. I have changed plugs and coils but it's still skipping. Its giving a code for closed loop, using o2 sensor for fuel mix. Any ideas on what I can do to fix the skipping? Also I have done a radiator flush changed thermostat and changed coolant sensor.