I have a Day &Night gas furnace and the gas flame will stay on for a few seconds and then shut off for several seconds. The pilot stays lit and the thermostat calls for heat. The blower continues running as the flame cycles. Any idea where to start trouble shooting?

Thanks for any help,
Greg

Is this the older furnace with an inducer motor(vent draft motor) and three wires going to the pilot assembly and five wires on the gas valve?