When early 450 SLs have a rough idle it can be vacuum leaks. The eight doughnuts under the intake manifold ducts are often dry and cracked introducing unwanted air to a factory preset mix of gasoline and air. This imbalance will create a lean miss-ﬁre behavior to occur to an otherwise well tuned 450SL engine. In fact all R107 V-8s from the 350 to the 560 engine can skip at idle because of these eight leaky intake manifold gaskets. A more subtle cause of a not so smooth idle on these early 450s can also be uneven valve adjustment clearance.