LS400 idle loops up and down from 1100rpm to 1600rpm every 3 seconds My 1990 LS400 runs high but even idle for approximately 15 seconds upon cold start. But then there is a moment when it changes... The idle goes up and down in a loop from 1100rpm gradually to 1600rpm then sharply drops back to 1100rpm every 2 or 3 seconds. When idle reaches 1600rpm the car makes subtle electric buzzing sound and idle goes sharply down to 1100 rpm... And it does it over and over again... Below is a recap of