'95 E420, Code 6, shes sick.

[AtlBenz]

1995 E420 with 144K on the clock.

code 6 is comming up which I beleive means something is up with the idle speed control....no? which makes sense taking into consideration the following symptom. there has been recent episodes where, during idle, the engine is, for lack of a bettter word, surging. rpms rise (though not past 1000 if i'm correct) and then plummet. the car "catches" these drops and I guess is trying to correct it. this results in the car almost, but not actaully stalling out. due to the rpm shift the engine and exhaust noise rises and falls to a deep, bassy shudder.

what do i have to replace?