I have a York furnace model # p2udd12p07601c. The problem I am having is when the funace starts up, occasionaly I can see the coil igniter light up and 30 seconds later or so the flame ignites by the igniter coil but only for a second and then it goes out without igniting across to the flame sensor. The exhaust fan will stay on, and a minute or so later the furnace will try to ignite again, and this time it ignites all the way across and everything seems to work fine. I had a service tech. come in and he cleaned the pilot tube between the igniter and the sensor, and cleaned the sensor, and it lit just fine every time he checked it. 2 days later I noticed it is doing the same thing. I am wondering what else it could be to make it ignite fine sometimes and not others. Any suggestions would be greatly appreciated.

Could be the burners and orfices need cleaning,, not a job for the novice