Gas and Oil Home Heating Furnaces - Trane XE 70 sparking 5 min before lighting

As my title says, my trane is sparking for about 5 minutes before it lights the pilot light. Following that, there are no other problems. The pilot ignites the burners, after about 2 minutes the blower comes on and it heats regularly to the set temperature. My question is if the cause of this would be the pilot valve causing a problem or if it is more likely something needs cleaned, or something else entirely. The thermostat is <1 year old digital and clicks the furnace on and off as scheduled. The problem started middle of last winter and is getting worse this winter as to how long it is before the pilot actually lights. Also, is it normal for the spark igniter to run the entire time the furnace is running? It is a 1987 model.

Try removing & cleaning the pilot burner. If the pilot burner is not the problem, I would have to suspect the gas valve.
No it is not normal for the ignitor to run the entire time the main burners are on. The most common cause of this is a dirty flame sensor. Sometimes the sensor & ignitor are one.

excellent. thanks for the info! I'm looking through the paperwork and it looks like the last service was done in 93. Also, when we moved in it had 20x16x1 filters in but it takes a 25x16x1. Called the guy that owned the house and he said he has always put in the 20s because "they are cheaper and it doesn't make a difference if a couple inches of air don't get filtered." Guess I have a weekend project to take out and clean the blower motor, pilot burner, and sensors.