Starting a car after sitting for months

My transmission went several months ago (maybe around 5-6 months ago). My car has been sitting under a carport that whole time except for two times when I drove it a few feet out so I could open the windows and have it air out in the sun. I noticed both times that when I did that the engine was revving up and down once I would put it in park. I'm not too worried about that, or at least I'm hoping there's no reason for me to be too concerned about that being that it has been sitting for a while. What I would like to know is I've decided to have my mechanic look into getting another transmission for it. Would it be okay for me to drive it to him when he gets one? He's about 4 miles down the road but I'm reading all of these horrible things that could happen to your engine if you run it with old gas and oil.