I would second the grounding issue: I would verify that both battery terminals are cleaned and the wires are securely fastened. There is a wire from the negitive terminal to the firewall that acts as a ground. It is relitively easy to access that spot, unbolt the ground, take some sandpaper to the paint at that spot and get down to bare metal. Rewire it up. It is amazing what odd behaviors this car will get if it is not getting sufficient ground. (For example my sons fiestas audio had bad noise in it. Sandpapering that spot fixed it)