Do you have any noticable loss in coolant or oil? Does it puff any kind of smoke out of the tailpipe or do you smell anything when warming it up? The head gaskets are notoriuous for leaking internally (oil seals also get hard and leak). It could be the warming up of the car might be the engine burning off the internal leaks in the leaky cylinders. The most improvement I had in starting and idle was after I replaced my O2 sensor. I tried the fuel accumulator idea as well and replaced the pumps and filter at the same time. Starting problem would still come and go. If it starts up pretty quick after you warm it up and then turn it off for a few minutes, then it could be the leakage. If it still has trouble starting and has to warm up, it probably has other issues as indicated by the other folks. Check the condition of your spark plugs and see if any look considerably different (worse) than the others. Unfortunately, if you don't get an expert W124 mechanic diagnosis, you may be tossing money at it until you eliminate the culprit.