I have a 97 chev suburban with a 5.7 vortec. When starting it cold or hot it reves up to about 1700 rpm for about 8-10 seconds then calms down to normal idle. It will also rev up when shifting out of park to drive when it has not been driven and is cold. This issue just popped up. The battery got worn down last weekend and i charged it back up but other than that nothing out of the ordinary. Any ideas as to what would cause it to rev up like this when starting and shifting?