Hello again David,
After seeing the diagram I am not recommending that you trouble shoot or work on that furnace yourself. It will not be an easy trouble shooting process, and there will be some risks that I do not recommend you take.
We will have to keep an eye on it, for now put some kind of spacer between the high tension sparking lead and sheet metal, the high voltage insulation breaks down a bit sometimes and can prevent sparking at the ignition rod... that would be a safe enough measure.
It is also possible that your furnace has a vent damper, as shown as an option on the wiring diagram, you may want to make sure the damper is opening if it has that option.
Beyond that measure this is likely to be a risky situation for you to attempt any repairs on, parts may not even be available. I do not recommend jumpering terminals 1 and 5 on the gas valve as a test in this case either.
Call those people on the phone monday, with the brand and model number of your furnace and ask if they have the spark ignition switch module and gas valve for that furnace... if they do not have it, it might be time to start thinking of a replacement furnace.
Keep me posted, we can go from there.