1973 450sl Stalling Problem

[R Ryan823]

My '73 450SL keeps stalling after about a half hour of driving. Sometimes after it stalls it will start right up. Other times I'm not as fortunate. I did a full tune-up (plugs,wires, etc) but still no luck. If I raise the idle RPM's to about 1,200 the problem goes away. I checked for any vacuum leaks. None found. My next step is to check the timing. I also saw in a previous thread that the idle control module might be the culprit. Before I spend a fortune on replacing that, I was wondering if anyone out there has had a similar problem and might know how to fix this. Any help would be appreciated.