Air Aspirator System: Description
2.2L and 2.5L EFI engines are equipped with an air aspirator valve. This valve uses exhaust pressure pulsations to draw fresh air from the air cleaner into the exhaust system. This reduces carbon monoxide and to a lesser degree, hydrocarbon emissions.
The air aspirator valve works most efficiently at idle and slightly off idle, where the negative exhaust pulses are strongest. The air aspirator valve remains closed at higher engine speeds.