High idle rev - low gas mileage on 2004 Pontiac Vibe

My average city gas mileage is 25 mpgs - not good, right? I have just tried cleaning the MAF, so I will see if there is a difference. Also, even in the summer, the startup idling rev's are close to 2,000 ... can I adjust this?

Asked by for the 2004 Pontiac Vibe