I have an 82 300sd and I have to cycle the glow plugs at least 3 times before it will start and idle fine. I am going to replace glow plugs soon and probably a block heater too.

Oh, what happens if the idle is too high or too low? also, what would cause the tranny to downshift hard?

ps, which glowplugs are best bosch or beru?
thanks -zach