1993 Ford Tempo

The temp gauge goes off the charts with the key on engine off but then would go down after the car was on. Ive herd of ect sensors being bad would then put ur fuel maps off allowing the car not to start. Also idles very high when it starts then comes down some times other time not. I get no response from the key in any position. No head lights. No trunk pop when button pushed no radio no automatic seat belt nothin. Thanks for your help