I have a 99 Sportage that is giving a 561 code that I am told means system voltage unstable, whatever the heck that means. When driving, it occassionaly just shuts down like someone turned of the key. It then takes a few minutes before it will start. The engine will just turn over as though there is no spark. It has 78K miles and the plugs were changed just a couple of months ago and has run great until right now. Any ideas?