All modular engines (gas engines in vans from '97 onward) have platinum plugs installed from the factory. They are good for AT LEAST 100,000 miles. An '02 Econoline van does not have plug wires, but eight individual coils one for each plug that sit directly on top of the plugs. They are prone to failure, and would cause this.
If your van has undre 36,000 miles on it, take it to the dealer and let them figure it out. If over, have it scanned for any codes, and repair as indicated (most likely there are misfire codes).