Erratic Idle Engine Speed with Air On while driving

I have a 2005 Vibe and have been noticing that with my air conditioner on, the engine idle speed will sometimes jump up to 1800+ RPMs. About the same range as a cold engine would be upon startup. Its most noticeable as I'm coming to a stop light or sign as I'm trying to stop, it feel as though someone is pushing me from behind. At the stop light or sign, I can put the car in neutral and the RPM's will be in the 1800-2000 RPM range for a very lengthy period of time or until I turn off the Air Conditioner. In addition, sometimes I can be driving at a constant speed with my Air on and my car will actually speed up without me depressing the gas pedal or if I take my foot off the pedal, as this is happening, the car will keep the same speed for an abnormal lengthy period of time before the engine idle speed starts slowing down. I took it to the dealer (under warranty), and they told me this is normal for this car which I find it hard to believe as I would think this would be a safety issue, causing the car to be harder to stop not the mention the extra wear and tear on your brake pad, but maybe that's the point from a service point of view. Anyway, anyone else run into this issue? Is the dealer just feeding me a line of BS?

My 05 base W/Auto acts similar in manner to what you've described. No real idea why the extreme but it is.