My furnace is pulsating, gas valve is clicking on and off rappidaly, I shut it off for a short time then it will work for a few hours then start acting up again installed new air pressure switch no change,do you think I should replace the flame sensor.

Intermittent operation/pulsing like this could be caused by the thermostat. Disconnect the red thermostat wire in the furnace low voltage area and see if it stops. If it does stop then you need to check the ow voltage wiring and the thermostat. If it continues then it would be best to call a professional since the problem can be serious.