I have a Trane furnace, model #BLU108F936B1. When the thermostat signals that it is time to provide heat, the bower comes on but the gas does not ignite. I am able at that time to light it with a match, and can hear the clicking sound accompanied by a weak spark. The furnace seems to work fine until the next time it demands heat. Could it be the ignition coil?

Your spark wire may be trying to ground out making the spark weak at the electrode. Dirty burners and crossovers will keep it from lighting also. If you can't get gas to the point of the spark, no ignition. Bad idea to use a match to light a furnace like that but I understand you got to do what you got to do.

Do a double check and make sure all the grounds are good,, sometimes a bad connection makes them not work well