I dunno if this is the right forum or not. I've asked around and found all different answers but here goes.

I've had my '02 WRX Wagon for a month now and from day one I noticed that it would idle really hard. The car would shake to the point of being uncomfortable at a stop light. It wasn't loud just shook really bad. Everyone told me that it was just the AC making fans turn on under the hood. Since the weather's been decent I've been driving with the windows down and AC off and sure enough the car idles fine. I'm a little worried though 'cause once it gets cold and I have to have the heat on it's gonna start back up. Is this rough idle a bad thing for the car? Is there any way to fix it so it doesn't do it? I've been told using synthetic oil will help make a smoother idle, I've been told to tighten the engine mounts. A little help would be greatly appreciated.