2 Intermittent codes

91 CRX HF w/ b16a... I get a 15 (Ignition Input) and a 17 (VSS) sometimes when I am coming to a stop, doesn't matter if I gear down or put it in neutral and coast. The new distributor is less than a year old and I replaced the speedometer cable with new about a year and half ago. Sometimes I drive a couple days without getting them and when I do, as soon as I turn the car off and back on, there gone.... could be for 3 miles or 3 days.

Car runs fine and the only thing I've changed is the stereo which I currently have unplugged and still get the codes.