I have noticed that when I take my GTS out it alway idles at 500rpm but as soon as I start driving and come to a stop, it idles at 1500rpm and sometimes it stays there. Why the variance in rpm's. Is this a sign of my intake manifold gaskets leaking? Its a 97 and has the original gaskets. It has not had any of the recalls performed. I hate looking like I am reving my engine every time a come to a light.