Emission Control problems of the 2004 Buick Rainier

With vehicle temperature at normal range, in park and at normal idle when I push on the gas pedal the rpm would drop to under 500 and then go back up, almost like a hesitation of sorts. Took vehicle to Buick dealer and was told that it was the secondary air pump, basically the egr valve. Was told this was part of the emissions of the vehicle but not covered under the emissions warranty nor would my extended warranty cover as well. Vehicle has 46,403 miles on it.