bmw 318i 85

engine idle up and down do anyone know the cause of this problem...?

bmw 318i 1985
have a problem with the engine idle control.
the engine runs fine until the motor get's hot then..
the up and down idle starts
ive heard this has been a know problem with some bmw's do anyone know the cause of this problem..?

could be plugs, wires, ignition, check these things.