There isn't a pat answer to your problem. Both the idle control function and lambda correction function must be monitored to diagnose the problem.
How close are you to Moorhead MN? I know someone there, competent and patient enough to get to the bottom of your problem.
I suspect that you are one of the luckiest and thus unluckiest of V8 MB owners. In 27 years of V8 chain failures (well into the hundreds), I have only seen 2 that only jumped 1 or 2 teeth. Your occurance is thus a very rare occurance to an experienced tech. I'm not condoning charging for poor diagnostics, but I could see it taking someone off guard.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician